The authors report a case of severe hyperkalemia (7 mmol/l) in an insulin-dependent diabetic in the absence of renal failure. This hyperkalemia was due to hypoaldosteronism caused by inadequate hormone biosynthesis in the absence of 21-hydroxylase. Replacement therapy allowed normalization of clinical and laboratory parameters. The various causes of hyperkalemia in the absence of renal failure in insulin-dependent diabetes are discussed, notably the renin deficiency hypoaldosteronism syndrome. This case study is remarkable for a number of reasons, including the very limited degree of virilization, the occurrence of a pregnancy, and the degree of salt excretion. This is a new observation in the diabetic, and is apparently a coincidental association since deficits in 21-hydroxylase are not usually associated with insulin-dependent diabetes.