Health political background Computerized physician order entry (CPOE) systems are software to electronically enter medication orders. They can be equipped with tools for decision support (CDS). In Germany, various vendors offer such systems for hospitals and physicians’ offices. These systems have mostly been developed during the last five to ten years. Scientific background CPOE-systems exist since the 1970’s. Usually, clinical decision support is integrated into the CPOE to avoid errors. Research questions This HTA-report aims to evaluate the effectiveness and efficiency of CPOE-/CDS-systems and their ethical, social and legal aspects. Methods The systematic literature search (27 international data bases) yielded 791 abstracts. Following a two-part selection process, twelve publications were included in the assessment. Results All reviews and studies included in the present report show that the use of CPOE-/CDS-systems can lead to a reduction of medication errors. Minor errors can be eliminated almost completely. The effect of CPOE-/CDS-systems on the rate of adverse drug events (ADE) is evaluated in only two primary studies with conflicting results. It is difficult to compare the results of economical studies because they evaluate different settings, interventions and time frames. In addition, the documentation often is not fully transparent. All four studies included measure costs and effects from the perspective of a hospital or hospital affiliation. Concerning social aspects, the literature points at changes regard competing interests of technology and humans that result from the implementation of CPOE-systems. The experience of institutions in which the implementation of CPOE-systems leads to problems showed that the importance of considering the socio-organisational context had partly been underestimated. Discussion CPOE-/CDS-systems are able to reduce the rate of medication errors when ordering medications. The adherence to guidelines, communication, patient care and personnel satisfaction can also be affected positively. However, the literature also reports negative effects, as through the use of CPOE-/CDS-systems new errors can be generated. This makes continuous revisions of the system, as well as data-updates necessary. Concerning the cost-benefit-ratio from the hospital perspective, the two qualitatively best economic studies show contradictory results. Therefore, a positive cost-benefit-ratio for individual hospitals cannot be assumed, particularly as the study results cannot be generalized. Conclusions If the implementation of CPOE-/CDS-systems is well planned and conducted, the system adapted to the needs of the institution and continuously reviewed, and data used are updated on a regular basis, the rate of medication ordering errors can be reduced considerably by using CPOE-/CDS-systems. However, it is not clear how this results in a reduction of ADE. Prospective, systematic multi-centre evaluation-studies with clear methodology are needed, which include an analysis of the user-friendliness and of social and technical aspects of the system. Such studies should evaluate the impact a CPOE-/CDS-system has on ADE-rates and mortality. A detailed description of the system used and of the hospital evaluated is essential. If possible, costs and cost effects should be surveyed and documented transparently.