Adolescents with obesity may engage in dieting to facilitate weight loss(1). However, dieting is also associated with eating disorder risk and body dissatisfaction. This study aimed to understand adolescent dieting behaviours and associations with eating disorder risk, weight bias internalisation and body appreciation. Adolescents (n = 141), median (IQR) age of 14.8 (12.9 to 17.9) years, mean (SD) BMI 35.39 (4.17) kg/m2, with obesity and ≥ 1 related complication were enrolled into the Fast Track to Health trial(2), which aimed to compare two dietary intervention. At the first dietetic visit, adolescents were asked whether they had previously seen a dietitian (yes or no) and if they had previously tried any diets; the types of diets tried were categorised. Self-report questionnaires including Eating Disorder Examination Questionnaire, Binge Eating Scale, Weight Bias Internalization Scale and Body Appreciation Scale were assessed. One-way ANOVA was used to investigate the difference in questionnaire scores based on the number of diets trialled (no diets, one diet, two/three diets). Of 141 adolescents enrolled, 68 (48.2%) had previously seen a dietitian and 106 (75.2%) had tried at least one diet. Most adolescents had tried one type of diet (n = 74, 52.5%), with 29 (20.6%) having tried two or three different diets. There were no associations between sex or age and history of seeing a dietitian or attempting to diet. Adolescent with a higher BMI, expressed as a percentage of the 95th percentile, were more likely to have seen a dietitian, but there was no association between BMI and the number of diets used. Adolescents who had tried two/three diets had higher scores on the Eating Disorder Examination Questionnaire compared to those who reported not dieting (mean [SD] 2.81 [1.12] vs 1.98 [1.08], p = 0.016). There were no differences in scores on the binge eating scale, weight bias internalization scale and body appreciation scale based on the number of diets trialled (p > 0.05). Many adolescents presenting to obesity treatment will have tried one or more diets with or without the support of a dietitian. Repeated dieting attempts may be an early indicator of eating disorder risk in this population. However, further research is needed to understand the duration of dieting and specific dieting practices used. Clinicians providing nutrition education and prescribing diet interventions should be aware of this and the potential influence on adolescent perceptions of healthy and unhealthy dieting practices.