We carried out a cross-sectional study to investigate factors associated with adherence to diet and medication in non-insulin-dependent diabetes mellitus (NIDDM) patients. A total of 200 patients not seeking treatment from clubs for diabetics from two hospitals in León, Mexico, accepted inclusion. Patients interviewed had a mean age of 58.8 (53.3-56.4, 95% C.I.) years. We evaluated adherence to diet and medication, knowledge on diabetes, social support, family's structure and functioning (with a modified McMaster model), metabolic control, and complications. Stepwise multiple regression procedure showed that adherence to diet was associated with years since diagnosis (p = 0.003) and with social support (p = 0.007). Adherence to medication was associated with social support (p = 0.002), and the age of the spouse (p = 0.016). Adherence to medication was lower in patients from families with rigid control than in the group with Laissez-faire type of control (p = 0.010) or the group with flexible control (p = 0.002). Social support was lower in the group with chaotic control than that in the group with flexible control (p < 0.001). Compliance to diet was associated with peripheral neuropathy and plasma creatinine, and adherence to medication with plasma glucose and peripheral neuropathy. We concluded that (1) adherence to treatment in NIDDM patients is associated with social support; (2) some aspects related to the family, such as the age of the spouse and the control of behavior, were also associated with compliance to treatment; and (3) it is important for the practicing physicians, and for institutional programs, to consider factors associated with adherence to treatment.