Findings from a research synthesis of the relationships between family needs and parent, family, and child functioning are reported. The synthesis included 31 studies conducted in 12 different countries. The studies were conducted between 1987 and 2021 and included 4,543 participants. Eight different family needs scales or adaptations of the scales were completed by the study participants (mothers, fathers, or grandmothers of children with developmental disabilities, autism spectrum disorders, or medical conditions). The outcome measures included caregiver psychological health, parenting stress, parenting burden, parenting beliefs, family coping strategies, family functioning, family support, and child functioning. The correlations between family needs and the outcome measures were used as the sizes of effects for evaluating the strength of the relationships between measures. Results showed that unmet family needs were associated with more negative and less positive family and family member functioning and fewer unmet family needs were associated with more positive and less negative family and family member functioning. The sizes of effect for parenting stress and burden were larger than were the sizes of effects for each of the other outcome measures. Child condition and study quality moderated the relationship between family needs and parenting stress and burden but not the other outcome measures. The results are discussed in terms of one component of family systems intervention models.