This paper explores individual, interpersonal- and household-level factors influencing HIV-related sexual risk behaviour among adolescent girls who participated in an intervention to reduce HIV risk in a rural setting in Mozambique. Twenty-eight adolescent girls ages 13-19, 30 heads of household, and 53 influential men participated in in-depth interviews at two time points. Comparative analysis compared girls who reported reducing risk behaviours over time to girls who did not and identified factors that respondents described as influential to behaviour change. Among the twenty girls self-reporting sexual risk at the first time point, half had reduced these behaviours one year later. Changes in girls' behaviours were contingent upon household- and interpersonal-level factors, particularly households' economic stability and family members' financial support. Future interventions with adolescents in similar settings should evaluate and leverage household and family support to achieve sexual risk reduction.