Diseases or physical disorders or infections that affect gay men disproportionately (but not exclusively) include:
HIV infection and AIDS
other sexually transmitted diseases (STDs) including:
herpes -- genital and oral
hepatitis A and B (vaccine preventable)
syphilis
gonorrhea
urethritis (which if untreated can lead to urethral stricture, epididymitis and abscess in the scrotum)
genital warts (condyloma acuminatum)
crabs (pediculosis pubis)
scabies
hepatitis C (possible)
molluscum contagiosum
"bugs" that can invade your gastrointestinal tract and are most often the result of oral/anal contact and include parasitic infections such as giardia and amebiasis and bacterial pathogens such as campylobacter, salmonella, and shigella
All of the above diseases need to be treated -- they cannot be ignored -- not only for your own sake but for the health of your sexual partners as well for they are communicable diseases. You've got them from somebody and you can give them to someone else.
In addition gay males are affected by ano-rectal disorders (though not necessarily the result of anal intercourse) that include:
anal fissures
hemorrhoids
anal abscesses
fistula-in-ano
anal skin irritation or itch
The penis can be infected bacterially by balanitis and the penis can be injured by:
phlebitis (blood clotting usually due to receiving rough and persistent oral sex)
phimosis and paraphimosis (disorders of the skin in uncircumcised males -- circumcision may be considered if the disorders persist)
priapism -- or the inability to lose an erection even after sexual feeling is gone. This condition can be caused by improper use of cockrings or drugs such as cocaine, alcohol and Viagra.
http://alwaysyourchoice.com/ayc/sex/gay/gmhintro.php