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Background: In 2010, Médecins Sans Frontières (MSF) discovered extensive lead poisoning impacting several thousand children in rural northern Nigeria. An estimated 400 fatalities had occurred over 3 mo. The US Centers for Disease Control and Prevention (CDC) confirmed widespread contamination from lead-rich ore being processed for gold, and environmental management was begun. MSF commenced a medical management programme that included treatment with the oral chelating agent 2,3-dimercaptosuccinic acid (DMSA, succimer). Here we describe and evaluate the changes in venous blood lead level (VBLL) associated with DMSA treatment in the largest cohort of children #5 y of age with severe paediatric lead intoxication reported to date to our knowledge. Methods and Findings: In a retrospective analysis of programme data, we describe change in VBLL after DMSA treatment courses in a cohort of 1,156 children #5 y of age who underwent between one and 15 courses of chelation treatment. Courses of DMSA of 19 or 28 d duration administered to children with VBLL $ 45 mg/dl were included. Impact of DMSA was calculated as end-course VBLL as a percentage of pre-course VBLL (ECP). Mixed model regression with nested random effects was used to evaluate the relative associations of covariates with ECP. Of 3,180 treatment courses administered, 36% and 6% of courses commenced with VBLL $ 80 mg/dl and $ 120 mg/dl, respectively. Overall mean ECP was 74.5% (95% CI 69.7%–79.7%); among 159 inpatient courses, ECP was 47.7% (95% CI 39.7%–57.3%). ECP after 19-d courses (n = 2,262) was lower in older children, first-ever courses, courses with a longer interval since a previous course, courses with more directly observed doses, and courses with higher pre-course VBLLs. Low haemoglobin was associated with higher ECP. Twenty children aged #5 y who commenced chelation died during the period studied, with lead poisoning a primary factor in six deaths. Monitoring of alanine transaminase (ALT), creatinine, and full blood count revealed moderate ALT elevation in ,2.5% of courses. No clinically severe adverse drug effects were observed, and no laboratory findings required discontinuation of treatment. Limitations include that this was a retrospective analysis of clinical data, and unmeasured variables related to environmental exposures could not be accounted for. Conclusions: Oral DMSA was a pharmacodynamically effective chelating agent for the treatment of severe childhood lead poisoning in a resource-limited setting. Re-exposure to lead, despite efforts to remediate the environment, and nonadherence may have influenced the impact of outpatient treatment. Please see later in the article for the Editors’ Summary. Citation: Thurtle N, Greig J, Cooney L, Amitai Y, Ariti C, et al. (2014) Description of 3,180 Courses of Chelation with Dimercaptosuccinic Acid in Children #5 y with Severe Lead Poisoning in Zamfara, Northern Nigeria: A Retrospective Analysis of Programme Data. PLoS Med 11(10): pmed.1001739. doi:10.1371/journal.pmed.1001739 Academic Editor: Bruce P Lanphear, Simon Fraser University, Canada Received September 16, 2013; Accepted August 19, 2014; Published October 7, 2014 This is an open-access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication. Data Availability: The authors confirm that, for approved reasons, some access restrictions apply to the data underlying the findings. Research data are accessible via the MSF open data policy for researchers who meet the criteria for access to confidential data (http://fieldresearch.msf.org/msf/handle/10144/306501). Funding: This study was funded as part of MSF operations. Lundbeck donated some DMSA, but had no role in the treatment programme or in study design, data collection and analysis, decision to publish, or preparation of the manuscript. The findings and conclusions in this presentation have not been formally disseminated by the Centers for Disease Control and Prevention/the Agency for Toxic Substances and Disease Registry and should not be construed to represent any agency determination or policy. Competing Interests: The authors have declared that no competing interests exist. Abbreviations: ALT, alanine transaminase; BD, twice daily; CaNa2EDTA, calcium disodium versenate; CDC, US Centers for Disease Control and Prevention; DMSA, 2,3-dimercaptosuccinic acid; DOT, directly observed therapy; ICPMS, inductively coupled plasma mass spectrometry; IV, intravenous; ECP, end-course venous blood lead level as a percentage of pre-course venous blood lead level; MSF, Médecins Sans Frontières; TDS, thrice daily; VBLL, venous blood lead level. * Email: Jane.Greig@london.msf.org PLOS Medicine | www.plosmedicine.org 1 October 2014 | Volume 11 | Issue 10 | pmed.1001739