BACKGROUND AND OBJECTIVE: Motivational interviewing (MI) has been shown to be an effective strategy for targeting obesity in adolescents, and parental involvement is associated with increased effectiveness. The aim of this study was to evaluate and compare the role of parental involvement in MI interventions for obese adolescents.

METHODS: A total of 357 Iranian adolescents (aged 14–18 years) were randomized to receive an MI intervention or an MI intervention with parental involvement (MI + PI) or assessments only (passive control). Data regarding anthropometric, biochemical, psychosocial, and behavioral measures were collected at baseline and 12 months later. A series of intention-to-treat, 2-way repeated-measures analysis of covariance were performed to examine group differences in change in outcomes measures over the 12-month follow-up period.

RESULTS: Results revealed significant effects on most of the outcome parameters for MI + PI (eg, mean ± SD BMI z score: 2.58 ± 0.61) compared with the passive control group (2.76 ± 0.70; post hoc test, P = .02), as well as an additional superiority of MI + PI compared with MI only (2.81 ± 0.76; post hoc test, P = .05). This pattern was also shown for most of the anthropometric, biochemical, psychometric, and behavioral outcome variables.

CONCLUSIONS: MI with parental involvement is an effective strategy in changing obesity-related outcomes and has additional effects beyond MI with adolescents only. These findings might be important when administering MI interventions in school settings.