This study examined the relationships among cortisol level and reactivity, illness, and behavioral measures in 21 day care children between 22 and 48 months of age. Children's temperament was measured by means of the Toddler Behavior Assessment Questionnaire (TBAQ) and the Goodfit Questionnaire, which were completed by parents and teachers. Over several weeks, children were screened for illness by a physician and a nurse and were diagnosed weekly. Salivary cortisol levels were measured both before and after children were presented with a mildly stressful task. Results for the cortisol measures indicated that: (1) baseline cortisol level was negatively correlated with teachers' Goodfit ratings of cheerfulness and sociability; and (2) cortisol level after the stressful task was correlated with parents' Goodfit rating of fussiness, and negatively correlated with teachers' Goodfit rating of cheerfulness. Results for the illness diagnoses indicated that: (1) withdrawal in the stressful task was correlated with respiratory infection, and negatively correlated with otitis media; (2) respiratory infection and overall illness were negatively correlated with the TBAQ rating of interest; (3) respiratory infection was correlated with teachers' Goodfit ratio of even-temperedness; and (4) respiratory infection and overall illness were correlated with parents' Goodfit rating of whinyness, but negatively correlated with teachers' rating. (BC)