Introduction Healthcare professionals (HCPs) and patients have various motives to report adverse drug reactions (ADRs) to their national agency. These motives may differ between countries. Objective The aim of this study was to assess to what extent motives of HCPs and patients to report ADRs differ between countries. Methods HCPs and patients from Croatia (HR), The Netherlands (NL), and the UK were asked to complete a web-based survey containing questions regarding demographics and ADR reporting. HCPs and patients could select all motives for reporting that applied to them, with a total of 23 and 24 motives, respectively. Descriptive statistics are presented and Chi-square tests were used to test for differences across the countries, with effect sizes calculated using Cramer's V. Results In total, 296 HCPs and 423 patients were included (60% and 32% from Croatia, 19% and 44% from NL, and 21% and 24% from the UK, respectively). For most of the motives to report or not to report an ADR, there were no differences between countries. Most HCPs from all countries would be motivated to report an ADR if there was a strong suspicion of causality (89%), if it concerned a severe/serious ADR (86%), and if it concerned an ADR for a new, recently marketed drug (77%). Most patients from all countries agreed that they would report an ADR if it concerned a severe ADR (96%), if the ADR influenced their daily activities (91%), and if they were worried about their own situation (90%). Differences across the countries (p V >= 0.21) were observed for three and four of the HCP and patient motives, respectively. For HCPs, these differences were seen in motives related to legal obligation (65% HR, 24% NL, 38% UK), black triangle medicines (27% HR, 4% NL, 77% UK), and the reporting of well-known ADRs (53% HR, 85% NL, 69% UK). For patients, these differences were seen in motives related to a linkage between the ADR report and the medical notes (59% HR, 60% NL, 30% UK), complexity and time taken to report (25% HR, 13% NL, 40% UK), medicines purchased on the internet (59% HR, 39% NL, 65% UK), and the reporting of embarrassing ADRs (32% HR, 11% NL, 35% UK). Conclusions HCPs' and patients' motives to report or not to report ADRs to the national agency were mostly similar across the three countries. Such motives can be used in general strategies to promote and increase ADR reporting. The observed differences provide guidance to further fine-tune ADR reporting at a national level.