Background: There is growing scientific interest in assessing the biological correlates of non-pharmacological interventions such as mindfulness. Examinations of the beneficial effects of mindfulness on hypothalamus-pituitary-adrenocortical system activity (HPA SA) and sleep are sparse. The aim of the present study was to explore the impact of long- and short-term meditation experience on HPA SA and sleep. Method: There were 20 participants, 9 of whom had long-term experience in meditation (mean = 264 months) and 11 novices. Novices underwent an 8-week course in Mindfulness-Based Stress Reduction (MBSR), and cortisol samples were taken in the lab at the beginning and end of the course. To assess the cortisol awakening response, 4 morning cortisol samples were collected. Sleep and mindfulness were assessed by self-rating questionnaires. Results: Among participants with long-term meditation experience, morning cortisol decreased with length of experience. For novices, after an 8-week introductory MBSR course, morning cortisol levels had decreased, while both sleep and self-attribution of mindfulness significantly improved. Cortisol levels did not, however, change between the beginning and end of individual MBSR sessions. Conclusions: The pattern of results lends support to the view that MBSR/meditation has a favorable influence both on biomarkers of stress regulation, such as cortisol secretion, and on sleep.