Thalidomide, an antiemetic administered in 60th of the 20th century to pregnant women, has become notorious for a range of adverse effects which led to its taking off market. In recent years, its antimyeloma effect was discovered. The aim of the work was to evaluate the incidence of adverse reactions to thalidomide. Its therapeutic effect has not been assessed because of a short period of monitoring and diversity of a sample. The assessed sample consisted of 17 patients with diagnosis of multiple myeloma (10 men and 7 women). An average age of patients was 62.9 +/- 9.4. An average time elapsed from making the diagnosis to starting the treatment with thalidomide was 51.0 +/- 23.7 months. An average length of therapy was 20.1 +/- 9.6 weeks. An average daily maximum therapeutic dose was 138.3 +/- 83.2 mg. Data were collected from outpatient physicians reports, regular laboratory tests, and direct interviews with patients. To classify severity of adverse drug effects (grades 0-4) we used WHO criteria, Cancer and Leukemia Group B criteria, and in cases where certain adverse effects were not included in the above mentioned criteria, we defined our own criteria. The most frequent adverse effects included: leucopenia or neutropenia in 12 (70.6%) patients, altered state of consciousness in 11 (64.7%) patients, obstipation in 10 (58.8%) patients, skin alterations in 9 (52.9%) patients, dizziness in 8 (47.1%) patients, peripheral neuropathy in 7 (41.2%) patients, spasms and spasmodic convulsions in 7 (41.2%) patients, and altered liver tests in 6 (35.3%) patients. From the perspective of necessity to interrupt treatment or reduce the dose the most severe disorders included: peripheral neuropathy in 2 patients (inability to control lower extremities), altered consciousness in 1 patient (protracted somnolence during a day), skin alteration in 1 patient (generalized toxoalergic reaction), leucopenia or neutropenia in 1 patient (1.0 resp < 0.5 x 10(9)/l), altered vision in 1 patient (blurred vision), hypothyroidism in 1 patient, and altered mood in 1 patient (subjective feeling of depression). This work proved thalidomide to be beneficial for the patients with multiple myeloma but it also shoved necessity to intensively monitor its adverse effects and to adjust its doses.