Urethral specimens from 172 men who attended sexually transmitted disease clinics in the Moscow Oblast were examined for Neisseria gonorrhoeae, Chlamydia trachomatis and Mycoplasma genitalium by nucleic acid amplification tests. N. gonorrhoeae was detected in the urethra of 41 (24%) of the 172 men and C. trachomatis in 57 (33%). The latter occurred in 15 (36%) of the 41 men who were infected by N. gonorrhoeae and in 42 (32%) of 131 uninfected by gonococci. Of the 42 men uninfected by gonococci but chlamydia infected, 39 (93%) had symptoms and/or signs of urethritis. M. genitalium was detected in 45 (26%) of the 172 men, in nine (22%) of the 41 men infected with N. gonorrhoeae and in 12 (21%) infected with C. trachomatis. M. genitalium was detected alone in 25 (28%) of the 89 men uninfected by either gonococci or C. trachomatis. Of these 25 men, 24 (96%) had urethral symptoms and signs of inflammation, a proportion significantly more than experienced by the 64 men uninfected by any of the microorganisms. Of the 31 men who apparently had no symptoms or signs of urethritis, only three (10%) were infected by M. genitalium. The data provide evidence for the pathogenicity and frequent occurrence of M. genitalium in men in Moscow and presumably elsewhere in Russia.