OBJECTIVE The incidence of occupational asthma (OA) is increasing worldwide. In this study, we first aimed to document the rate of diagnosis of OA among patients who were referred to our clinic from the Social Security Institution and the factors that affected diagnosis; secondly, we aimed to assess the consistency of the medical and legal diagnoses. METHODS The study involved 132 consecutive patients who were referred to our clinic for the evaluation of OA between 2010 and 2015. Detailed workplace history, the tools used in the diagnosis such as peak expiratory flow (PEF) monitoring and bronchial provocation tests, and the final medical diagnosis were recorded from case files. RESULTS Asthma was diagnosed in 75% (n = 99) of the patients. Among them, 22.2% were diagnosed as having OA. The diagnosis was confirmed by serial PEF measurements, non-specific bronchial hyperreactivity assessment or both of the tests both at work and off-work periods. OA diagnosis was mostly established in active workers (72.7%). The legal diagnosis period was completed in 54.5% of these 22 patients, and 50% (n = 11) were officially diagnosed as having OA with a 91.6% concordance with medical diagnosis. CONCLUSIONS This study verifies the importance of diagnosing asthma correctly as a first step in the evaluation of OA. Diagnostic tests other than specific provocation tests could be preferential in patients who still work in the same field. We believe that cooperation with the patient's occupational physician and adequate recognition of the work environment will improve the consistency of legal and medical diagnoses.