An analysis of the renin-secreting tumors published in the literature suggests the diagnosis of JGC tumor should be evoked systematically in a young patient with severe hypertension and hypokalemia in whom a renovascular lesion has been eliminated by arteriography. A very high PRA usually is observed and blood pressure drops during converting enzyme treatment. Under acute administration of captopril, plasma renin may or may not increase, showing the inconsistency of the secretory autonomy of the tumor. The most useful examination for the localization of the tumor is the CT scan. Excessive renin production may provoke vascular lesions, left ventricular hypertrophy, and impairment of renin function that all disappear after surgical treatment, at the time when blood pressure returns to normal. Primary reninism has great physiologic importance for the hypothesis that favors the essential role of the kidney in determining the level of blood pressure. It can be considered as a unique, purely renin-dependent form of hypertension. This syndrome has no experimental equivalent and is the most caricatural form of other renin-dependent hypertension, such as renovascular disease, and probably some other forms of essential hypertension. The discovery of a renin-secreting tumor therefore constitutes a life-saving diagnosis for the patient, a subject of reflection for the specialist, and a useful tool for studies of the general mechanisms involved in enzyme biosynthesis and tumoral endocrine cell function.