BACKGROUND: The causes of health inequalities are complex. For the reduction of health inequalities, intersectoral collaboration between the public health sector and both social policy sectors (e.g. youth affairs, education) and physical policy sectors (e.g. housing, spatial planning) is essential, but in local practice difficult to realize. The aim of this study was to examine the collaboration between the sectors in question more closely and to identify opportunities for improvement. METHOD: A qualitative descriptive analysis of five aspects of collaboration within sixteen Dutch municipalities was performed to examine the collaboration between the public health sector and other policy sectors: 1) involvement of the sectors in the public health policy network, 2) harmonisation of objectives, 3) use of policies by the relevant sectors, 4) formalised collaboration, and 5) previous experience. Empirical data on these collaboration aspects were collected based on document analysis, questionnaires and interviews. RESULTS: The study found that the policy workers of social sectors were more involved in the public health network and more frequently supported the objectives in the field of health inequality reduction. Both social policy sectors and physical policy sectors used policies and activities to reduce health inequalities. More is done to influence the determinants of health inequality through policies aimed at lifestyle and social setting than through policies aimed at socioeconomic factors and the physical environment. Where the physical policy sectors are involved in the public health network, the collaboration follows a very similar pattern as with the social policy sectors. All sectors recognise the importance of good relationships, positive experiences, a common interest in working together and coordinated mechanisms. CONCLUSION: This study shows that there is scope for improving collaboration in the field of health inequality reduction between the public health sector and both social policy sectors and ...