Background: Many patients who consult their GP are worried about their health, but there is little empirical data on strategies for effective reassurance. To gain a better understanding of mechanisms for effective patient reassurance, we explored cognitions underlying patients' worries, cognitions underlying reassurance and factors supporting patients' reassuring cognitions. Methods. In a qualitative study, we conducted stimulated recall interviews with 21 patients of 12 different GPs shortly after their consultation. We selected consultations in which the GPs aimed to reassure worried patients and used their videotaped consultation as a stimulus for the interview. The interviews were analysed with thematic coding and by writing interpretive summaries. Results: Patients expressed four different core cognitions underlying their concerns: 'I have a serious illness', 'my health problem will have adverse physical effects', 'my treatment will have adverse effects' and 'my health problem will negatively impact my life'. Patients mentioned a range of person-specific and context-specific cognitions as reasons for these core cognitions. Patients described five core reassuring cognitions: 'I trust my doctor's expertise', 'I have a trusting and supporting relationship with my doctor', 'I do not have a serious disease', 'my health problem is harmless' and 'my health problem will disappear.' Factors expressed as reasons for these reassuring cognitions were GPs' actions during the consultation as well as patients' pre-existing cognitions about their GP, the doctor-patient relationship and previous events. Patients' worrying cognitions were counterbalanced by specific reassuring cognitions, i.e. worrying and reassuring cognitions seemed to be interrelated. Conclusions: Patients described a wide range of worrying cognitions, some of which were not expressed during the consultation. Gaining a thorough understanding of the specific cognitions and tailoring reassuring strategies to them should be an effective way of achieving reassurance. The identified reassuring cognitions can guide doctors in applying these strategies in their daily practice.