The research investigated the effect of mindfulness meditation on the emotional states of depression, anxiety, and stress. Additionally, we explored whether people with varying severity of depression, anxiety, and stress responded differently to mindfulness training. In order to investigate these questions, participants (n = 50) completed the Depression Anxiety and Stress Scale, 21-item version (DASS-21) before and after a 10-week mindfulness meditation program. As predicted, the severity levels of all affective measures have decreased by the end of the meditation course. Participants with severe emotional difficulties at the time of commencing the meditation course demonstrated the most notable improvement over time. These results suggest that mindfulness training is beneficial in reducing the symptoms of subclinical depression and anxiety and can substantially reduce stress. Attentional retraining and self-management aspects of mindfulness meditation, as well as relevant methodological issues are discussed.