Little is known about factors associated with treatment initiation in overweight and obese adolescents. This study investigated parent-reported adolescent demographic, adolescent health, and parent motivation factors associated with initiation of a family-based adolescent overweight and obesity intervention. A telephone survey was completed by 349 parents calling to register their interest in participating in a cognitive behavioral lifestyle intervention for adolescent overweight and obesity. A total of 172 families (49.3%) returned their consent form to initiate treatment. A binomial logistic regression, with predictors entered in three blocks: (i) adolescent demographic (adolescent age, gender, adolescent BMI-for-age z-score, parent BMI); (ii) adolescent health (perceived adolescent physical and mental health, presence of an adolescent physical health problem or mental health problem, medication intake); and (iii) parent motivation (perceived adolescent weight category, concern about adolescent weight, importance of adolescent weight, confidence in adolescent capacity to change weight, priority of adolescent weight loss, discrepancy between adolescent current and ideal weight, previous weight loss attempts), was significant (χ2 (16) = 35.19, P = 0.004) accounting for 12.4-16.5% (95% confidence interval) of treatment initiation variance. Parent-reported adolescent physical health problem, parent perception of adolescent weight category, parent priority of adolescent weight loss, and parent perception of discrepancy between adolescent current and ideal weight were significant in the model. These findings indicate that data collected at intake are associated with treatment initiation and highlight the role of assessing and enhancing treatment motivation from initial contact.