BACKGROUND Symptoms and health problems caused or aggravated by work are common. In order to study perceived work ability and associated factors, including those related to work, a closer analysis was undertaken in an occupational health setting. OBJECTIVE This study aimed to analyse self-assessed work ability and its determinants in employees seeking medical advice, with special emphasis on work-related factors. METHODS During 723 illness-related visits to occupational physicians, questionnaires covering personal data, main health problems, their work relatedness, duration and effect on work ability were completed by the employee and physician. Factors associated with self-assessed work ability were studied in a multinomial logistic regression model. RESULTS The majority of employees considered themselves as being able or partially able to work despite the health problem. Independent predictors of impaired work ability were mental or musculoskeletal disorders, self-assessed work relatedness of the disease, older age, blue-collar work and short duration of the symptoms. If the patient was convinced about the benefits of work-related interventions, the risk for disability was significantly reduced. CONCLUSIONS Special attention should be paid to the recognition and modification of potential work-related causes of disability. In addition, patients with partial work ability should be encouraged to stay at work instead of taking sick leave. For effective disability management, accommodated work and other evidence-based interventions are needed at the workplace.