OBJECTIVE: Administration of nonsteroidal antiinflammatory drugs (NSAIDs) may impair fertility. The occurrence of the luteinized unruptured follicle (LUF) syndrome was assessed in women with inflammatory arthropathies exposed to NSAIDs and compared to that in nonexposed women. METHODS: Fourteen patients with inflammatory rheumatic disease, 29 women with noninflammatory musculoskeletal conditions, and 449 women not exposed to NSAIDs were studied by intravaginal ultrasound monitoring for follicular development and ovulation in 1 or more menstrual cycles. Disease activity was assessed in inflammatory rheumatic disease. RESULTS: In 59 monitored cycles of patients with continuous NSAID exposure, 35.6% of LUF syndromes occurred compared to 3.4% of LUF syndromes in untreated women (P