Background: Earlier studies have shown poor documentation of the reasons for medication discontinuation during hospitalization. Communication of reasons for discontinuation, e.g. adverse drug reactions (ADRs), to general practitioners and pharmacists was also found to be insufficient, leading to a rate of represcription after an ADR of 27 % during the first 6 months after discharge. Objective: The aim of this study was to develop and implement a user-friendly electronic clinical decision support system to document reasons for medication discontinuation in hospitalized geriatric patients and to flag potentially undesirable represcriptions. Methods: The electronic clinical decision support module was developed using the Gaston framework. Pop-up windows force physicians to document reasons for medication discontinuation, and the system alerts physicians to the represcription of drugs withdrawn because of an ADR. We interviewed users regarding the acceptability of the system. Results: On a 20-bed geriatric ward, the electronic system documented 2,228 medication discontinuations and the reasons for them over 11.4 months and alerted physicians to represcription of drugs associated with an ADR 20 times. The system was considered to be user-friendly. Conclusions: This clinical decision support system fulfilled its aims of documenting the reasons for medication discontinuation and alerting physicians to potentially undesirable represcription of previously withdrawn drugs. It was found to be user-friendly.