Stress and negative affective states are associated with cortisol in everyday life. However, it remains unclear what types of stressors and which affective states yield these associations, and the effect of trait anxiety is unknown. This study investigates the associations of specific task-related stressors and negative affective states in everyday life with salivary cortisol, and explores the mediating and moderating role of state negative affect and trait anxiety, respectively. Salivary cortisol, subjective stress, and state negative affect were measured three times a day on 2 days in 71 participants in everyday life, using a handheld computer to collect self-reports and time stamps and an electronic device to monitor saliva sampling compliance. Stress measures comprised the experience of performance pressure and failure during daily tasks; measures of negative affect comprised worn-out, tense, unhappy, and angry. Effects were tested using multilevel fixed-occasion models. Momentary performance under pressure was related to higher momentary cortisol measures, while mean task failure was related to lower daily cortisol concentrations. The association of performance pressure with cortisol varied between subjects, and this variation was explained by trait anxiety, yielding stronger associations in participants scoring high on trait anxiety. No evidence was found for a mediating role of state negative affect. These results describe the well-documented associations of everyday stressors and affect with salivary cortisol more precisely, suggesting that performance pressure is a significant condition related to short-term changes in cortisol. Subjects scoring high on trait anxiety seem to process stress-relevant information in a way that amplifies the association of performance pressure with reactions of the hypothalamus-pituitary-adrenal axis.