Objective: To investigate the effects of oral testosterone undecanoate (TU) on symptoms associated with late-onset hypogonadism (LOH). Design: Multicenter, randomized, double-blind, placebo-controlled. Methods: The study was performed in 14 study centers in seven European countries. Men R50 years (nZ322) with symptoms of hypogonadism and testosterone deficiency (calculated free testosterone !0.26 nmol/l) were randomized and treated for 12 months with placebo or oral TU 80, 160 or 240 mg/day. Primary outcome was the total score on the Aging Males' Symptoms (AMS) rating scale after six months of treatment. Results: Treatment of mild-to-moderate LOH symptoms in subjects with borderline hypogonadism with oral TU resulted in an improved total AMS score at month 6, but differences between groups were not statistically significant. There was greater improvement in subjects !60 years when compared with subjects R60 years (PZ0.001), but baseline testosterone level had no influence on treatment response. The AMS sexual symptoms domain improved with oral TU 160 mg/day at months 6 (PZ0.008) and 12 (PZ0.012) compared with placebo, but not with 80 and 240 mg/day. Treatment was well-tolerated and there were no between-group differences in adverse events or drop-out rates. Conclusions: In one of the largest placebo-controlled studies of testosterone therapy in LOH, oral TU did not improve total AMS score in subjects with mild-to-moderate symptoms compared with placebo, except the sexual symptom sub-domain where a modest improvement was reported with oral TU 160 mg/day.