Men who have sex with men (MSM) often create sexual agreements with their partners, but little is known about agreements with serious versus causal partners. We used data from 472 young MSM to examine agreements with one's most recent partner, individual differences across types of partnerships and agreements, and predictors of condomless anal sex (CAS). Two-thirds of participants did not have agreements. Monogamous agreements were most common among those who were seriously dating their partner, but also present among those who were casually dating their partner and those who were not dating their partner. Participants who were seriously dating their partner reported the most frequent sexual health communication. Participants without agreements reported the lowest frequency of and comfort with sexual health communication. Participants who were seriously dating their partner and those with monogamous agreements were most likely to report CAS. HIV prevention should address communication with serious and casual partners.