Fabry's disease was diagnosed in an adult patient as a lipid storage-induced non-obstructive hypertrophic cardiomyopathy. Stable angina pectoris started 15 years before death, was followed by slowly progressive heart failure and repeated pulmonary thromboembolism with death at 63 years. Autopsy disclosed enormous cardiomegaly (1100 g), cardiac storage of ceramide trihexoside (CTH) of the same intensity as in classical cases of generalized Fabry's disease (11 mg lipid/g wet weight) restricted to cardiocytes. Other tissues (liver, kidney, brain, pancreas, pulmonary artery, coronary arteries) were free of storage. Using proton magnetic resonance analysis on formaldehyde-fixed tissue the stored CTH was identified as globotriaosylceramide. It was enzymatically degradable by control cell cultures but left uncleaved by mutant reference Fabry cells. Alpha-galactosidase activities in peripheral leucocytes of all four of the patient's daughters were in the heterozygous range. The diagnostic difficulties in this monosymptomatic novel variant of Fabry's disease are stressed.