Significantly more individuals with human leucocyte antigens (HLA) A9 and B27 have been identified in the group of chronic paranoid schizophrenics with early onset of the disease. It is known that individuals with HLA B27 have a markedly increased risk to fall ill from arthropathies (i.e. Bechterew’s disease). Generally, it seems extremely rare that arthropathies and schizophrenia occur together in the same person. In 16 chronic paranoid schizophrenics with HLA B27 no form of arthropathy and in 288 arthropathic patients no case of schizophrenia could be detected (evidenced in a psychiatric case register). Furthermore in 131 arthropathic patients with HLA B27 no psychiatric disease (except one feebleminded and one with alcohol problems) could be identified. On the other hand, in the group of arthropathic patients without HLA B27 the incidence of psychiatric diseases was 5 times higher than in the group with HLA B27 and so comparable to the morbidity of the normal population. It is conceivable that HLA B27 is a ‘genetic marker’ for arthropathy as well as for a defined subgroup of schizophrenia. These data agree with the hypothesis that schizophrenia and arthropathies are mutually exclusive in one indiv