The article is an analysis of 3 clinical cases, characterized by the presence of the lumbosacral axial involvement, with the radiological evidence of a bilateral sacroiliitis and a peripheral polyarthritis displaying a rheumatoid picture, with rheumatoid factors in the serum and in 2 of the cases also in the articular fluid. These cases belong to the HLA-27 B histocompatibility type, a feature which could be, according also to the data of literature, an explanation of the association of these two diseases.