PURPOSE: To study possible differences in trust between general practitioners (GPs) and occupational physicians (OPs) and the explanatory factors for trust. Insight into the factors predicting trust can improve programmes for stimulating the co-operation of GPs and OPs. THEORY: On the basis of theories of trust and of social identity theory we expected, (1) in both professions a higher level of knowledge-based trust than of identification-based trust, (2) a relationship between higher levels of identification-based trust and higher frequency of contact, (3) OPs to have a higher level of identification-based trust than GPs. We hypothesised (4) that OPs perceiving an equal status have higher levels of trust and (5) GPs perceiving a higher status have lower levels of trust. METHODS: A mail survey sent to 2297 doctors (1728 GPs and 569 OPs) of which we used 547 questionnaires. RESULTS: Hypotheses 1 and 2 were supported. Hypothesis 3 was not supported. Hypotheses 4 and 5 were supported for knowledge-based trust. On the basis of these findings it is possible that co-operation between the two groups is still in its early stages. CONCLUSIONS: Programmes to improve the co-operation of GPs and OPs should focus on equalising status and stimulating contacts to build (identification-based) trust.