The isotope strontium-89 (^89Sr) was used for the first time in 1941. It was the focus of many studies in which the effectiveness of treating pain caused by bone metastases was confirmed. It is considered as a safe drug, but not without side effects. Haematological complications (e.g. bone marrow suppression) may be dangerous. The aim of the study was to assess the severity of this type of side effect using our own material. It was a retrospective study of 15 cases of ^89Sr treatment. We compared counts of erythrocytes, white blood cells, and platelets before treatment and on two control visits. The first visit was 21 ±6 days after treatment, and the second one was an average of 51 ±9 days after treatment. In our own material, toxicity grade 3 or 4 in relation to white blood count did not occur in any patient. Toxicity grade 3 PLT between 25,000 and 49,000 occurred in two patients on the second visit. When qualifying according to guidelines the treatment is safety. As the disease progresses, the blood morphology and bone marrow reserve decrease. This points to the necessity to refer patients in the early stage of painful bone metastatic disease for ^89Sr treatment.