The frequency of Sjögren's syndrome (SS) was evaluated in 45 patients with rheumatoid arthritis (RA). Subsequently, the clinical, biological and evolutive profiles of RA associated or not with SS were compared. The prevalence of definitive SS was 55%, while in 24% isolated data of gland involvement were found. The variables related with the development of SS in patients with RA were: sex, functional respiratory parameters, and, basically, the duration of RA. The latter relationship had a uniform association model, i.e., the prevalence of SS increased in a constant fashion following the duration increments of RA. The change of patients from negative to definite SS was uniform throughout the evolution of RA.