A retrospective investigation of the prescription of nonsteroidal antiinflammatory drugs (NSA) was performed in the Rheumatologic out-patient-institute in Zagreb, including 1000 patients of both sexes, aged 20-70 years. 500 outpatients were treated by NSA during 1987 and 1989 respectively for lumbosacral syndrome, rheumatoid arthritis, ankylosing spondylitis and coxarthrosis. The kind of NSA as well as the registered side-effects were analysed from case histories. During 1987, NSA were applied to 365 (73%) and during 1989 to 390 (78%) of the 500 patients. In both groups a phenyl-acetic acid derivative (diclophenac) was most often applied, followed by propionic acid derivatives and oxycams. The most rarely applied drugs were indol-acetic acid derivatives. Pyrazolones were given only to 2 patients with an acute flare of ankylosing spondylitis in 1987. A gastro-duodenal ulcer was the absolute counterindication for this kind of treatment. The number of side-effects in this investigation was relatively small (6.5% in 1987 and 5% in 1989), probably because this investigation was a retrospective one. The most common among them appeared in the gastro-intestinal tract.