['Most adolescents and young adults (AYAs) with type 1 diabetes struggle with diabetes self-management and exhibit suboptimal glycemic control. This study examined two models of association between illness representations, a modifiable predictor of suboptimal outcomes, and adherence and glycemic control in AYAs with type 1 diabetes.', 'Ninety-nine AYAs (ages 15-20\u2009years) completed measures of illness representations and adherence at two visits. Blood glucose monitoring frequency and haemoglobin A1c were obtained via chart review. Relationships were examined using structural equation modelling.', 'Illness representations accounted for a significant proportion of the variance in blood glucose monitoring frequency (ΔR2 =\u2009.23, p\u2009<\u2009.01) and adherence to emergency precautions at Time 1 (ΔR2 =\u2009.07, p\u2009=\u2009.03). Illness representations also accounted for significant variance in blood glucose monitoring frequency (ΔR2 =\u2009.08, p\u2009=\u2009.01), adherence to recommendations for insulin and food (ΔR2\u2009=\u2009.08, p\u2009=\u2009.02) and exercise (ΔR2 =\u2009.10, p\u2009<\u2009.01), and adherence to emergency precautions (ΔR2)=\u2009.16, p\u2009<\u2009.01) at Time 2.'] Do illness representations predict adherence in adolescents and young adults with type 1 diabetes?