Pregnancy, motherhood, and HIV infection in adolescence are events with relevant biological, psychological, and social implications for mothers, their babies, and families. Our study aimed to identify protective factors of the experience of pregnancy and motherhood among young mothers living with HIV, highlighting similarities and differences. A mixed method multiple-case study was conducted with three young primiparous mothers (ages 17 to 19 years), whose babies were 4 to 6 months old. Participants were recruited from specialized care services in Porto Alegre, Brazil. Data were collected using social support and adherence-to-treatment questionnaires and a semi-structured interview. The following protective factors were identified: positive feelings about motherhood, positive assessments of received care and couple relationships, disclosure of HIV diagnosis to family members, family support, and accountability for infant care. Longitudinal studies would enhance the understanding of these factors, particularly if carried out with adolescents of different ages and focused on coping strategies.