The incidence of bone marrow involvement in sarcoidosis patients and changes in their peripheral blood parameters have been investigated. Out of 92 patients diagnosed with sarcoidosis at our center between 1994 and 2002, 50 (54.3%) gave consent for a bone marrow biopsy and were included into our study. The clinical features, peripheral blood parameters and bone marrow biopsy findings of the patients were analysed. Of these 50 patients, 39 were females and 11 were males (median age 37 years, range 16-62). Anemia was detected in 11 (22%) cases, and both anemia and leucopenia in 3 (6%). In 10% (5 patients; 3 males, 2 females) of the patients, bone marrow biopsy revealed noncaseified granulomas. Sarcoidosis patients with bone marrow involvement had higher incidences of extrapulmonary involvement, leucopenia-lymphopenia and anemia than those without involvement (P values were, 0.05, 0.001 and 0.06, respectively). Of the 11 patients with anemia, 3 had involvement of the bone marrow by sarcoidosis and 7 had iron deficiency anemia. As a result, bone marrow involvement should be considered in sarcoidosis patients with anemia, leucopenia-lymphopenia, and also extrapulmonary involvement.