Objective: We retrospectively investigated the relationship between newborn male circumcision (NMC) and second to fourth digit ratio with penile length in young adult. Design and Method: We evaluated that the patients who had history of the circumcision at past visited our hospital for urological treatment. The age at which the circumcision had been done was assessed. The patients’ heights and weights were measured. Second to fourth digit ratio was calculated by measuring the second and fourth digit lengths. The flaccid and erectile penile lengths were measured from the base of the penis to the tip of the glans in standing position. Results: A total of 248 patients finished our study. The subjects were divided into two groups, including 72 patients in the NMC group, and 176 patients in the non-NMC group. In univariate analysis, height, second to fourth digit ratio, flaccid penile length and age of circumcision were associated with erectile penile length. Flaccid (p<0.001) and erectile (p=0.001) penile lengths were shorter in the NMC group than in the non-NMC group. Among these variables, second to fourth digit ratio, flaccid penile length and age of circumcision were a significant predictive factor for erectile penile length in multivariate analysis. Conclusions: Second to fourth digit ratio, flaccid penile length and the age of circumcision were significant predictive factors for erectile penile length. Furthermore, penile lengths were shorter in the NMC group than in the non-NMC group.