Clinical and morphologic findings are described in 17 patients who died suddenly and unexpectedly during or shortly after use of the liquid-protein-modified-fast diet. Of the 17 patients, 16 were women, most were young (average age 37 years), and most lost a massive amount of weight (average 41 kg or 35% of their prediet weight) over a short period of time (average 5 months). Eight had one or more episodes of syncope. Multiple-lead ECGs were recorded in 10 patients. All had normal sinus rhythm; all had episodes of ventricular tachycardia; nine and possibly 10 patients had prolongation of the QT interval, unassociated with the recognized causes of QT interval prolongation in at least seven of the nine patients; and nine had diminished amplitude of the QRS complexes ('low voltage'). Histologic study of left ventricular myocardium in 14 patients disclosed attenuated myocardial fibers in 12, increased lipofuscin pigment in 11, and mononuclear-cell myocarditis in one. Similar histologic findings, however, also were found in 16 cachetic control subjects studied in similar fashion, but ECGs in them showed no prolongation of QT intervals or episodes of ventricular tachycardia. Thus, semistarvation, particularly in the face of antecedent obesity, is a cause of acquired QT interval prolongation, and repeated ECGs are recommended in patients on semistarvation diets for treatment of obesity.