Psychiatric illness course is not characterized by total regularity. More often there is marked individual variability. This is an obstacle to making a valid prognosis and applying broadly based indication rules. Still today predictors of illness course as well as indication criteria for treatment are little elaborate and often faile in the individual case. The most reliable instrument for planning and assessing psychiatric treatment is the treatment course itself. The therapist as a participating observer can more easily check tendencies of illness course and adapt therapeutic strategies. Characteristics of treatment course in guiding further treatment are examplified by means of neuroleptic treatment in the acute and maintenance phase of schizophrenic psychoses.