To evaluate the adequacy of pharmacological thromboembolic prevention in the medical ward of a university hospital, we performed a retrospective study in 227 consecutive inpatients. The presence of risk factors, and type, length, and dose of pharmacological prevention were documented by chart review. Only 22% of the 153 risk patients received adequate prevention, whereas 38% of the patients at low risk were given pharmacological prophylaxis. The high prevalence of over- and undertreatment is an indicator of less than optimal care. Quality of care interventions, such as the development of local guidelines, might improve the appropriateness of pharmacological thromboembolic prophylaxis in medical inpatients.