The pathological changes in muscles biopsied from 2 brothers with rigid spine syndrome are reported. The findings ranged from marked fascicular atrophy and fibrosis to hypotrophy of small groups of fibres and vacuolation in most fibres. The presence of vacuoles and deposits of accumulated material seemed to be common to all the biopsies. These findings, compared with those reported in the literature, confirmed the histopathological heterogeneity of this syndrome but proposed also the hypothesis that similar elementary lesions of muscle fibres can account for the initiation of the pathological process, developing asynchronously in different muscles because of their different activity.