Little is known about the factors and outcomes associated with young people’s subjective relationship assessments. Understanding what young people think makes their relationships ‘good’ or ‘bad’ would give us insight into what is important to them in their relationships as well as their decision-making and behaviour within them. Self-report data from 757 girls (mean age = 17.09 years) and 642 boys (mean age = 17.23 years) were analysed using logistic regression. Relationship primacy was significantly associated with positive relationships for girls and boys. Among girls, partner education and open communication about sexual and reproductive health were additionally related to relationship assessments. Among boys, very little quarrelling was the only additional factor associated with positive relationship assessment. Although relationship assessment was not associated with depression or problem drinking for either girls or boys, drug use was less likely among both girls and boys who reported having a positive relationship. Boys in positive relationships were also more likely to have used a condom the last time they had sex with their main partner. Intervention programmes should equip teenagers with skills to develop and maintain positive relationships.