Objective To measure patient safety culture in Belgian hospitals and to examine the homogeneous grouping of underlying safety culture dimensions. Methods The Hospital Survey on Patient Safety Culture was distributed organisation-wide in 180 Belgian hospitals participating in the federal program on quality and safety between 2007 and 2009. Participating hospitals were invited to submit their data to a comparative database. Homogeneous groups of underlying safety culture dimensions were sought by hierarchical cluster analysis. Results 90 acute, 42 psychiatric and 11 long-term care hospitals submitted their data for comparison to other hospitals. The benchmark database included 55 225 completed questionnaires (53.7% response rate). Overall dimensional scores were low, although scores were found to be higher for psychiatric and long-term care hospitals than for acute hospitals. The overall perception of patient safety was lower in French-speaking hospitals. Hierarchical clustering of dimensions resulted in two distinct clusters. Cluster I grouped supervisor/manager expectations and actions promoting safety, organisational learning–continuous improvement, teamwork within units and communication openness, while Cluster II included feedback and communication about error, overall perceptions of patient safety, non-punitive response to error, frequency of events reported, teamwork across units, handoffs and transitions, staffing and management support for patient safety. Conclusion The nationwide safety culture assessment confirms the need for a long-term national initiative to improve patient safety culture and provides each hospital with a baseline patient safety culture profile to direct an intervention plan. The identification of clusters of safety culture dimensions indicates the need for a different approach and context towards the implementation of interventions aimed at improving the safety culture. Certain clusters require unit level improvements, whereas others demand a hospital-wide policy.