Background Relationships between anthropometric measures, body proportions, weight and penile dimensions in young adult males have not been previously analysed. Furthermore, although male fertility declined in last decades, no data on testicular volume (the best surrogate measure for spermatogenic potential) is available for the general population of young men in Italy. Aim To analyze for anthropometric measures and proportions, testicular volumes, and penile dimensions a large cohort from the general population of young Italian men aged 18-19 years. Materials/subject We analysed 2019 students aged 18-19 years for height, weight, body mass index (BMI), waist circumference, arm span, pubis-to-floor and crown-to-pubis length, and penile dimensions. Testicular volumes were measured by ultrasound in 776 subjects. Results Subjects with a pathological arm span - height (>3 cm) were 36.0% and those with a pathological pubis-to-floor/crown-to-pubis ratio (≤0.92) were 44.7%. The mean penis length was 8.9 ± 1.4 cm and the penis circumference was 9.5 ± 1.0 cm. BMI was positively associated with arm span - height difference and negatively with penis length. The rate of subjects with low mean testicular volume (<12 mL) was 23.2%. Conclusions The findings highlight a strong influence of BMI on skeletal proportions and penis length, identify a large proportion of subjects with testicular hypotrophy at risk for future fertility, and suggest to consider worldwide studies to redefine normal values for arm span - height and upper/lower body segment ratio.