Sex hormones appear to play a pivotal role in determining cardiovascular risk. Androgen deprivation therapy for males with prostate cancer results in a hypogonadal state that may have important, but as yet undetermined, effects on the vasculature. We studied the effects of androgen deprivation therapy on large artery stiffness in 22 prostate cancer patients (mean age, 67 ± 8 yr) over a 6-month period. Arterial stiffness was assessed using pulse-wave analysis, a technique that measures peripheral arterial pressure waveforms and generates corresponding central aortic waveforms. This allows determination of the augmentation of central pressure resulting from wave reflection and the augmentation index, a measure of large artery stiffness. Body compositional changes were assessed using bioelectrical impedance analysis. Fasting lipids, glucose, insulin, testosterone, and estradiol were measured. After a 3-month treatment period, the augmentation index increased from 24 ± 6% (mean ± SD) at baseline to 29 ± 9% (P = 0.003) despite no change in peripheral blood pressure. Timing of wave reflection was reduced from 137 ± 7 to 129 ± 10 msec (P = 0.003). Fat mass increased from 20.2 ± 9.4 to 21.9 ± 9.6 kg (P = 0.008), whereas lean body mass decreased from 63.2 ± 6.8 to 61.5 ± 6.0 kg (P = 0.016). There were no changes in lipids or glucose during treatment. Median serum insulin rose from 11.8 (range, 5.6-49.1) to 15.1 (range, 7.3-83.2) mU/liter at 1 month (P = 0.021) and to 19.3 (range, 0-85.0 mU/liter by 3 months (P = 0.020). There was a correlation between the changes in fat mass and insulin concentration over the 3-month period (r = 0.56; P = 0.013). In a subgroup of patients whose treatment was discontinued after 3 months, the augmentation index decreased from 31 ± 7% at 3 months to 29 ± 5% by 6 months, in contrast to patients receiving continuing treatment in whom the augmentation index remained elevated at 6 months compared with baseline (P = 0.043). These data indicate that induced hypogonadism in males with prostate cancer results in a rise in the augmentation of central arterial pressure, suggesting large artery stiffening. Adverse body compositional changes associated with rising insulin concentrations suggest reduced insulin sensitivity. These adverse hemodynamic and metabolic effects may increase cardiovascular risk in this patient group.