Low serum testosterone levels are common in aging men and are associated with decreased muscle mass and bone mineral density, increased adiposity, and insulin resistance. Shores et al used a clinical database to identify men 40 years or older who had low, normal, or equivocal (both low and normal) testosterone levels. Risks for all-cause mortality were estimated using Cox proportional hazards regression models for a follow-up period of up to 8 years. Compared with men with normal testosterone levels, men with low testosterone had an 88% increased mortality risk after controlling for age, medical morbidity, and other clinical covariates. To minimize the effect of acute illness on the results, an additional analysis was done excluding men who died within the first year, and low testosterone levels continued to be associated with a significantly increased mortality risk.