The hypothesis that negative affectivity (NA) is associated with accuracy of blood glucose (BG) symptom perceptions and diabetes control was assessed. After completing measures of BG symptom beliefs and NA-related constructs (i.e., attentional focus and trait anxiety), 35 adolescents with insulin-dependent diabetes monitored their physical symptoms and their actual BG levels 3 times daily for 2 weeks. Each subject's actual BG symptoms were determined by correlating symptom ratings with BG levels and were then compared with symptom beliefs. Those who were more internally focused were more able to discern which symptoms actually covaried with BG fluctuations; those with higher trait anxiety tended to misattribute non-diabetes-related symptoms to BG levels. Finally, interactions suggested that those who both attend to internal physical sensations and experience-heightened anxiety display poorer metabolic control.