To investigate the follow-up of the 17 patients during the period of 1995-2001 of the outpatient Clinic for Rheumatology at the University Hospital of Zurich with arthritis and the presence of parvovirus B19 DNA demonstrated by PCR in synovial biopsies. Seventeen patients of 163 with arthritis, which were routinely examined by needle arthroscopy during 1995-2001 with a positive parvovirus B19 DNA by PCR of synovial biopsy were reevaluated. Investigations included medical history, clinical examination and blood tests. Joint fluid was taken on patients with joint effusion. The observation period of the 17 patients (F:M = 11:6) was 2-8 years (Ø = 6.5 years). In 8 of 17 patients the arthritis could not be classified neither at entry nor during the follow up of the study. The arthritis could be diagnosed in six patients early in the onset of the disease and included three cases of lyme arthritis of the knee joint, two cases with arthritis following a gastrointestinal infection (one with Salmonella typhimurium--positive faecal test--and the other one with a culture negative agent), one patient probably had an infection-associated arthritis after a gastrointestinal infection with Entamöeba histolytica (Schirmer et al. in Rheumatol Int 18:37-38, 1998; Kasliwal in Am J Proctol Gastroenterol Colon Rectal Surg 32:12, 16, 28, 1981; Haslock and Wright in J R Coll Phys Lond 8:1554-162, 1974; Than-Saw et al. in Trop Geogr Med 44:355-358, 1992) with remission after antibiotic therapy. After a disease course of 9 months one patient could be classified as rheumatoid arthritis in the presence of anti-cyclic citrullinated antibodies but lack of rheumatoid factor. One patient with polyarthritis developed psoriasis of the skin 22 months later. From the nine patients with unclassified arthritis 4 (45%) got into complete remission with no symptoms or signs of joint inflammation after a disease course of 9-45 months, whereas 5 (55%) still demonstrate active non erosive arthritis (disease duration between 3 and 10 years). The presence of parvovirus B19 DNA in synovial tissue of patients with joint inflammation does not allow the diagnosis of parvovirus induced arthritis. If the arthritis remains unclassified and without erosions over time a virus associated aetiology may be assumed. However, no definitive diagnosis is possible even in the presence of parvovirus B19 DNA in synovial tissue.