Teachers constitute one of the professional collectives most affected by psychological problems. The purpose of this quasi-experimental study is to examine the efficacy of a mindfulness training programme to reduce psychological distress in a group of teachers. The sample comprised 68 teachers of Secondary School Education, from various public schools; half of them formed the experimental group, and the another half the control group. The levels of psychological distress were measured, in both groups, by the Symptom Checklist-90-R (SCL-90-R) before and after the application of the programme. Statistical analysis shows the significant reduction of three general measures of psychological distress (Global Severity Index, Positive Symptom Distress Index, and Positive Symptom Total), as well in all its dimensions (somatization, obsessive-compulsive, interpersonal sensibility, depression, anxiety, hostility, phobic anxiety, paranoid ideation, and psychoticism), in the experimental group compared with the control group. Follow-up measures show that these results were maintained for four months after termination of the intervention in the experimental group.