- Sick-leave certification (SLC) is a legal document that provides official work exemption. In Israel, all SLCs are issued by primary care physicians. When providing a SLC, physicians are influenced by medical as well as nonmedical issues, such as the patients' psychosocial state and their workplace characteristics. To evaluate the explicit and implicit reasons for a SLC in Israeli primary care practices. A case-control prospective study was conducted in 47 urban primary care clinics in Israel. Patients of working age who received a SLC and a control group of consecutive patients without a SLC were included. Patients were interviewed by phone using a structured questionnaire, regarding their socio-demographic background, the duration of the SLC, their workplace characteristics, and their self-rated health status. The doctors completed a consent form, signed by the patients, incLuding the explicit and the implicit reason for providing a SLC. Data was obtained from 918 patients; of these patients, 560 received a SLC and 358 were controls. The average duration of the SLC was 5.49 +/- 8.22 days, with a median of 3 days. The main explicit reasons for a SLC were: an acute medical problem (50%), and the patient's request (40%). The physicians' implicit reason was mainly the patient's request (84%). Self-employed workers and workers who do not receive payment for a full months work had significantly fewer SLCs. A Logistic regression model found younger age, salaried workers, entitlement for sick leave, special payment for a full months work, visiting for an acute illness or a request for SLC were the main factors significant in SLC provision. Providing SLCs is a common task of primary physicians in Israel Most SLCs are for a short time, up to 3 days. Family physicians usually accept their patients' request for a SLC. Workplace regulations influence patients' and physicians' behaviors related to SLCs.