In a review of the literature from 1948 to 2001, 122 studies were found that correlated structural or functional social support with patient adherence to medical regimens. Meta-analyses establish significant average r-effect sizes between adherence and practical, emotional, and unidimensional social support; family cohesiveness and conflict; marital status; and living arrangement of adults. Substantive and methodological variables moderate these effects. Practical support bears the highest correlation with adherence. Adherence is 1.74 times higher in patients from cohesive families and 1.53 times lower in patients from families in conflict. Marital status and living with another person (for adults) increase adherence modestly. A research agenda is recommended to further examine mediators of the relationship between social support and health.