Since the year 2000, Danish rheumatologists have been collecting data on a routine basis in the nationwide DANBIO registry, which includes all rheumatologic patients receiving biological drugs. Demographic data, markers of disease activity, current treatment, serious and non-serious adverse events and reasons for discontinuation are registered at each visit either on paper forms or on-line. By June 2005, approximately 3000 treatment courses (18,000 visits) were in the registry, corresponding to close to 90% of eligible patients. Rheumatoid arthritis was the most prevalent diagnosis (75%) followed by ankylosing spondylitis (11%) and psoriatic arthritis (7%). Infections occurred in 43% of the treatment series.