The descriptive study examined the role of peer influence and tertiary institution type on attitude toward cohabitation among adolescents in southwestern Nigeria. A sample of 620 males and females with (M=19.56 years, SD=6.18) completed a survey that comprised demographic information, measures of attitude toward cohabitation and peer pressure. Findings revealed that there was significant influence of peer influence on attitude toward cohabitation. There was no influence of tertiary institution type on attitude toward cohabitation. The study concluded that peer influence was a major determinant of attitude toward cohabitation. The study therefore recommended that psychologists should give proper orientation to students on the destructive tendencies that peer influence could have on their intention to have positive attitude toward cohabitation.