Two clinico-pathological cases of Kearns-Sayre syndrome are reported. In both cases the typical triad (progressive external ophthalmoplegia, heart block, retinitis pigmentosa) was present and spongiosis was the main pathological finding. In one case there was also a marked capillary proliferation, significance of which is discussed. A deletion of the mitochondrial DNA was found in the muscle, spinal cord and brain of this last case.