Objectives This paper aims to describe the degree to which general practitioners (GPs) explore suicidal behaviour among depressed patients in the Netherlands. Design An observational study of consultations between GPs and depressed patients. Setting 39 sentinel GP practices within the Netherlands in 2017. Participants Patients with a registration of depression. Primary and secondary outcome measures Primary outcome measure is suicide exploration by the GP. Secondary outcome measures at patient level, assessed by surveying GPs, include prevalence and severity of suicidal thoughts. Secondary outcome measures at GP level include follow-up actions of GP and reasons not to explore suicidality. Results A total of 1034 questionnaires were included in the analyses. GPs assessed and explored suicidality in 44% of patients with depression (66% in patients with a new episode of depression). GPs explored suicidal feelings more often in patients with a new episode of depression (OR 4.027, p<0.001, 95% CI 2.924 to 5.588), male patients (OR 1.709, p<0.001, 95% CI 1.256 to 2.330) or younger patients (OR 1.017, p<0.001, 95% CI 1.009 to 1.026). Multilevel analysis showed that 22% of the variation in suicide exploration is due to differences in GP practice. Thirty-eight per cent of the patients who were asked by their GP, reported (severe) suicidal ideation. Most GPs (68%) did not explore suicidal feelings because they thought the patient would not be suicidal. Conclusion GPs explored suicidal thoughts in less than half of all depressed patients and in two-thirds of patients with a new episode of depression. Suicide prevention training is recommended to enhance suicide exploration.