This paper is the first in a planned series of papers studying the effectiveness of psychotherapy and counselling in Nairobi. It describes a method for checking the effectiveness of psychotherapy and improving service quality in a Kenyan context. Rather than prematurely imposing psychotherapy protocols developed in Western countries in another cultural context, we believe that first studying psychological interventions as they are practised may generate understanding of which psychological problems are common, what interventions therapists use, and what seems to be effective in reducing psychiatric problems. The initial step is to assess outcome of psychological treatments as they are conducted. This is followed by statistical analyses aimed at identifying patient groups who are not improving at acceptable rates. Therapists will then be trained in a 'best practice' approach, and controlled trials are used in a final step, testing new interventions specifically targeted at patient groups with sub-optimal outcomes.