It is generally recognized that testicular volume reflects spermatogenic potential and testicular function. In adults, despite normal puberty, testicular volume varies considerably. There is still no rational explanation for this phenomenon. In view of this, Dr. Oh et al. from the Department of Urology, Gye Hospital, Gachon University and Seoul National University Hospital, Korea, hypothesized that finger formation during fetal life may be related to testicular development and testicular volume, and investigated the relationship between finger proportions and testicular volume in adults, which was published in the recent issue of the journal Andrology. The vertebrate Hox gene family is known to play an important role in limb and genital development. In particular, the Hoxa and Hoxd genes are essential not only for finger growth and development but also for genital bud differentiation. Previous studies have shown that the ratio of finger 2 to finger 4 (finger ratio) may be associated with male reproductive system function or disease. The authors prospectively enrolled 172 Korean men (aged 20-69 years) hospitalized for urological surgery. Patients with conditions known to significantly affect testicular volume were excluded. Before measuring testicular volume, the lengths of the 2nd and 4th fingers of the patient’s right hand were measured by an investigator using a digital vernier caliper. Without knowing the finger ratio of the patient, testicular volume was measured by an experienced urologist using a testicular meter. It was found that age, height, serum testosterone and free testosterone levels did not correlate with testicular volume. In contrast, finger ratio and body weight were significantly correlated with testicular volume (Figure 1). Fig. 1 Relationship between finger ratio and testicular volume. Right and left finger ratios were significantly and negatively correlated with testicular volume. Multivariate analysis using linear regression modeling showed that finger ratio alone was an independent predictor of all (right, left, and total) testicular volumes, whereas age, weight, and testosterone concentration were not independent predictors of testicular volume. The testes have an important role in the male reproductive system and their volume size can be used as an indicator of male fertility. The results of this study showed that finger ratio was negatively correlated with adult testicular volume, i.e., men with large finger ratios were likely to have smaller testes compared to men with small finger ratios.