This study examined changes in cognitive complexity and symptomatology in psychotic and non-psychotic patients undergoing psychotherapy. Grid technique was used to measure differentiation and integration, representing cognitive complexity. Two studies found that at therapy end, patients simplified their cognitive systems, with decreases in differentiation and integration. Symptomatology also significantly decreased. For non-psychotic patients, decreases in differentiation correlated with improved symptoms. A psychosocial intervention for psychotic patients similarly found decreases in integration/differentiation and symptoms over two years. The findings suggest psychotherapy helps simplify patients' cognitive systems as symptoms improve.