AIMS: We studied the international classification of disease (ICD) hospital discharge codes to find unreported adverse drug reactions (ADRs), and asked doctors about their attitudes to reporting some of these cases. METHODS: We examined the ICD codes assigned on discharge to identify ADRs and compared these with spontaneous reports made to the Committee on Safety of Medicines (CSM). Doctors involved were sent brief résumés of cases and asked if they would report them. RESULTS: 49 of 21 365 patient episodes were coded on discharge as ADRs, of which 33 were 'reportable'. Fourteen spontaneous reports were received by the CSM during the same period. The two groups did not overlap. 25 of 60 doctors responded to our questionnaire, and would have reported only 8 of 75 cases outlined. CONCLUSIONS: The ICD coding allowed us to identify important ADRs which most doctors would not report spontaneously.