Male hypogonadism is characterized by a lowering of plasma testosterone level below the lower limit of physiological variations. Conversely, some adult males, apparently eugonadic, have a plasma testosterone level much higher than normally. In most cases, male hypertestosteronaemia - defined by a plasma testosterone level above 13 ng/ml and due to various physiopathological mechanisms - is part of a wider pathological context. It betrays hyperandrogenism (elevated free testosterone) during treatment with androgens or chorionic gonadotropic hormone. In other cases, it seems to underlie a relative hypoandrogenism with rise of testosterone bound to transport proteins and/or excess of oestrogens. Hypertestosteronaemia therefore appears as a biochemical sign not to be ignored, but it also suggests that men with abnormally high testosterone levels present with new pathology and that aetiological investigations are necessary.