ABSTRACT Background: Intellectual disability (ID) and autism spectrum disorder (ASD) are often concomitant childhood developmental disorders. These disorders can alter family quality of life (FQoL). Objective: To investigate FQoL among families who have children with mild ID, associated with mild ASD. Methods: Cross-sectional descriptive study with 69 families who have children with mild ID and ASD, ranging from six to 16 years old, and who were provided with disability-related services in Brazil. Data were collected using a family sociodemographic questionnaire, an ID and ASD personal profile form, the Barthel index for activities of daily living and the Beach Center FQoL scale. Results: People with ID and ASD had an average score of 88.2±11.5 in the Barthel index, thus indicating moderate dependency in basic activities of daily living. The average total FQoL score (3.56±0.34) was lower than the scores for the “family interaction” (3.91±0.42; p<0.001), “parenting” (3.79±0.35; p<0.001) and “disability-related support” (3.98±0.16; p<0.001) domains; and higher than the scores for the “physical/material well-being” (3.19±0.64; p<0.001) and “emotional wellbeing” (2.75±0.62; p<0.001) domains. Parents’ marital condition, monthly family income, family religious practice and effective communication skills among the people with ID and ASD were predictors for FQoL (R2=0.407; p<0.001). Conclusions: FQoL was sustained through factors such as family interaction and parents’ care for their children. Improving families’ emotional wellbeing and physical and material conditions is likely to positively affect the FQoL of these families.