OBJECTIVES: Ankylosing spondylitis (AS) is a progressive, incurable rheumatologic disease with worldwide prevalence of 0.1-0.5%. Since January 2012, the Brazilian Agency for Supplementary Healthcare (ANS-Agência Nacional de Saúde Suplementar) declared the coverage of intravenous biological drugs (BD) mandatory for patients with AS, rheumatoid arthritis, psoriatic arthritis and Crohn’s disease in the private healthcare system (PHS). This study presents real-word data on the patterns-of-care for AS in Brazilian PHS. METHODS: We retrieved all requests of BD for patients with AS submitted between January/2012-January/2015 on Evidências-Kantar Health private market administrative claims database. After patient de-identification, data on diagnosis, type of drug, and line-of-treatment were collected.  RESULTS: BD was requested for 46 patients, 16 males (34.8%) and 30 females (65.2%), mean age of 43.7 years. Drugs requested were: infliximab (39.1%), adalimumab (21.7%), golimumab (19.6%), etanercept (17.4%) and rituximab (2.2%). Most patients (73.9%) were on first-line treatment with BD, 23.9% on second and 2.2% on third-line. Reasons for change in medication were: unsatisfactory response (75%) and adverse events (25%). Based on available information, diagnosis of AS couldn't be confirmed for all patients. For 52.2% AS was the most likely diagnosis, other possible diagnoses were: primary sacroiliitis (17.4%), degenerative spine disease (4.3%), unspecific lumbar pain (4.3%), enteropathic arthritis (4.3%), Reiter’s syndrome (2.2%) and seronegative arthropathy (2.2%). In 13% of the cases, lack of information precluded diagnosis. In 4 of 16 cases in which AS was not the most likely diagnosis, patients were already on 2^nd or 3^rdline treatments due to unsatisfactory response. CONCLUSIONS: Choice of BD followed international guidelines for AS. However, almost half the patients could not have diagnosis of AS confirmed, even tough some were already on 2^nd or 3^rd line therapy with BD. PHS must emphasize the correct use of diagnostic criteria before patients are put on unnecessary treatment with BD.