Background: The majority of studies support modern assertive health service models. However, the evidence is limited for parts of continental Europe, as well as for the pharmacological adherence outcome parameter. Method: We conducted a quasi-experimental controlled trial including adult patients with a schizophreniform disorder and a maximum of 60 points on the Global Assessment of Functioning Scale (GAF). Interventions (n = 176) and controls (TAU, n = 142) were assessed every six-month within one year in 17 study practices in rural areas. Mental and functional state were rated using the Brief Psychiatric Rating Scale (BPRS) and the GAF. Functional limitations and pharmacological adherence were patient-rated using the WHO-Disability Assessment Schedule II (WHODAS-II) and the Medication Adherence Report Scale (MARS). We computed multilevel mixed models. Results: The GAF and BPRS of both groups improved significantly, yet the increase in the intervention group was significantly higher. In contrast, patient-rated variables-WHODAS-II and MARS-neither showed a stable temporal improvement nor a difference between groups. Conclusion: Our findings only partly support the investigated AO intervention, because of conflicting results between clinician- and patient-ratings. Accordingly, the benefits of AO need to be further evaluated.