Possible data complicating sex hormones, especially testosterone, in the etiology of cardiovascular disease and noninsulin-dependent diabetes mellitus (NIDDM) comes from the much higher rates of cardiovascular disease in men than in women. Pharmacological administration of anabolic steroids to both men and women increases glucose and insulin concentrations and also insulin resistance. In vivo assessment of sex hormones and binding proteins in both premenopausal and postmenopausal women has suggested that increased free testosterone and decreased sex hormone-binding globulin (SHBG) is associated with higher glucose and insulin concentrations. In a few studies, increased insulin resistance has been associated with decreased SHBG levels. Some data suggests that visceral fat mediated the associates of sex hormones with insulin in women. Little prospective data is available on the association of sex hormones to the development of NIDDM in women but in two studies, low SHBG concentrations predicted NIDDM in Gothenburg and San Antonio. Recently, attention has focused on the role of sex hormones in relation to insulin in men. Surprisingly, higher levels of testosterone have been associated with improved cardiovascular risk factors (such as high-density lipoprotein cholesterol) and lower glucose and insulin levels. Total testosterone and SHBG have been associated with defects in nonoxidative glucose disposal and upper body adiposity in normoglycemic Finnish men. The latter observation is of interest since specific defects in nonoxidative glucose disposal are observed in normoglycemic relatives of subjects with NIDDM. The temporal relationship between sex hormones and insulin has been controversial. The traditional view of sex hormones increasing insulin resistance has been challenged in women by studies showing that insulin stimulates androgen production in the ovary. Recent data [JCEM 1995;80:654-658] suggests that insulin stimulates testosterone production and suppresses SHBG production in normal and obese men. On the other hand, administration of testosterone to centrally obese hypogonadal middle-aged men has improved insulin sensitivity.