The authors reviewed the files of male patients who have been hospitalized over a 12 year period for a rheumatoid-factor negative arthritis beginning after age 50. Polymyalgia rheumatica, psoriasis or crystal-induced arthritis were excluded. The remaining 105 observations were classified according to published criteria in rheumatoid arthritis (RA), reactive arthritis or ankylosing spondylitis (AS). Twenty-nine patients had RA and 29 had AS with equal numbers of axial and peripheral types. Four patients had reactive arthritis, one of them had also AS. Forty-four patients had "unclassified arthritis". Among the latter, 14 were B27 positive, 21 were B27 negative, 9 were not typed. Some features were more frequent in B27+ patients: an assymetrical oligoarthritis of the lower limbs with minimal signs of inflammation at synovial analysis or at synovial biopsy; frequent unilateral edema; marked, constitutional signs; very high ESR. Nine patients, all B27+, met the diagnostic criteria of spondylarthropathy. B27 typing thus appears relevant to the classification of late-onset, seronegative rhumatisms.