Previous research has found an increase in healthcare costs before psychotherapy, followed by a decrease thereafter—a pattern also observed in our sample. However, research on the patterns of change is still lacking. Healthcare quarterly cost patterns of change were examined in a field study of 1508 patients before and during outpatient psychotherapy. Several models assess the patterns of change of the entire sample and in subgroups of those undergoing prolonged psychiatric treatment versus the rest. An exponential pattern (increasing rate of change) had the best fit during the waiting period for the prolonged psychiatric treatment group. A linear pattern was selected for the rest. A logarithmic pattern (decreasing rate of change) best fits the prolonged pharmacotherapy group during therapy. A linear pattern was selected for the rest. The economic implication of the findings is that the prolonged psychiatric treatment group is expected to have the highest return on investment when the waiting period for treatment is shortened. This unique pattern of change may also be a marker of increasing distress in this group while waiting for treatment and the rapid effect that the start of psychotherapy has on this. Therefore this group should be the focus of attention.