INTRODUCTION Pharmacists can play a fundamental role in adverse drug reaction (ADR) reporting, although the factors that affect underreporting among these professionals are unknown. The objectives of this study were to identify (i) professional or demographic characteristics; and (ii) attitudes associated with pharmacists' ADR reporting in northern Portugal. METHODS We conducted a case-control study on a population of pharmacists employed in hospital and community pharmacies across Portugal's Northern Regional Health Authority catchment area in 2003. Cases (n=34) comprised pharmacists who had reported at least one ADR to the northern region's drug surveillance unit, and controls (n=280) were randomly sampled from pharmacists who had never reported an ADR. All were interviewed using a mail questionnaire. Most attitudes were based on Inman's 'seven deadly sins' and were measured using a continuous visual analogue scale. Answers were recorded in a range from 0 (total disagreement) to 10 (total agreement). Logistic regression was used to determine the ADR reporting adjusted odds ratio (OR) for a change in exposure corresponding to the interquartile range for each attitude. RESULTS The response rate was 86.8%. Reporting probability proved higher among hospital versus community pharmacists (adjusted OR 20.0; 95 CI 3.3, 125.0; p<0.001). Attitudes to ADRs were strongly associated with reporting probability. Hence, an interquartile decrease in any of the following attitudes increased the probability of reporting by (i) 223% (95% CI 51, 595; p < 0.05) for "Really serious ADRs are well documented by the time a drug is marketed"; (ii) 240% (95% CI 89, 508; p=0.002) for "I would only report an ADR if I were sure that it was related to the use of a particular drug"; (iii) 316% (95% CI 44, 1104; p=0.010) for "It is only necessary to report serious or unexpected ADRs"; and (iv) 171% (95% CI 13, 549; p=0.020) for "I do not have time to think about the involvement of the drug or other causes in ADRs". CONCLUSIONS ADR under-reporting is strongly associated with certain attitudes, possibly indicating that under-reporting could be minimised through educational interventions targeted at changing such attitudes. Pharmacists' ADR education must be improved and educational programmes should be focused on altering attitudes identified by the study as being associated with under-reporting. Our data also indicate that community pharmacists must be a priority target for this intervention.