Engaging beneficiaries in family-centred interventions is a well-documented challenge. Programme engagement evidence is limited for low- and middle-income countries. This study assessed the effect of incentives on participant engagement in a family-centred HIV prevention programme among caregiver and adolescent groups in KwaZulu Natal. Incentive packages were randomly assigned by site, ranging from optimal (to address major structural barriers) to basic (routinely provided by organisations serving vulnerable youth). Attendance rates for 490 caregivers and their 583 adolescents were measured. Cross tabulations of attendance and incentive data demonstrated the highest level of caregiver attendance and programme completion among groups receiving optimal incentives.