Ibrutinib is approved in Japan for the treatment of chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma (SLL) based on the results of global and domestic clinical studies. Following approval, we conducted an all-case post-marketing surveillance in Japanese patients with relapsed/refractory CLL/SLL newly initiated on ibrutinib treatment between May 2016−September 2017. Of the 323 patients enrolled, the safety and efficacy analysis sets comprised 289 and 205 patients, respectively. The overall response rate with ibrutinib treatment was 64.4%, and the estimated 52-week progression-free survival (PFS) and overall survival (OS) rates were 71.7 and 79.1%, respectively. No significant difference in the PFS rate was observed among patients with and without del(17p) (P = 0.160); however, PFS was significantly longer in patients who received 1 prior line of therapy versus >1 prior lines of therapy (P = 0.007). Adverse events occurred in 74.0% of patients, and typically occurred early (≤12 weeks) after ibrutinib initiation, followed by a decline in incidence thereafter. The overall rates of infection, bleeding, and arrhythmia were 22.5, 12.8, and 4.8%, respectively. Grade ≥3 bleeding events and atrial fibrillation occurred in 2.4% of patients each. The efficacy and safety profile of ibrutinib treatment in routine clinical practice was consistent with clinical trials and previously reported domestic data. UMIN-CTR Clinical Trials Register ID: UMIN000021963.