OBJECTIVE: Physicians' use of Motivational Interviewing (MI) techniques when discussing weight with adolescent patients is unknown. METHODS: We coded audio-recorded encounters between 49 primary care physicians and 180 overweight adolescent patients. During weight discussions, we used the MITI 3.0 to assess: Empathy, MI Spirit, open-ended questions, reflections, MI consistent behaviors (e.g., praising) and MI inconsistent behaviors (e.g., confronting). We examined associations of patient and physician characteristics with (1) MI techniques, (2) time discussing weight, and (3) encounter time. RESULTS: Physicians used more MI consistent techniques with female patients (p=0.06) and with heavier patients (p=0.02). Physicians with prior MI training also used more MI consistent techniques (p=0.04) and asked more open-ended questions (p=0.05). Pediatricians had a higher MI Spirit score than family physicians (p=0.03). Older patient age was associated with physicians spending less time discussing weight-related topics (p=0.04) and higher BMI percentile was associated with physicians spending more time discussing weight-related topics (p=0.01). Increased use of MI inconsistent techniques was associated with longer encounters (p=0.02). CONCLUSION: Physicians' weight discussions vary based on adolescent and physician characteristics. Importantly, not using MI lengthened encounter time. PRACTICE IMPLICATIONS: Physicians might consider using MI techniques more and attempt to use these equally with all adolescents.