Instruments for external quality assurance in inpatient parent-child rehabilitation and prevention facilities were developed in 2 projects. For the assessment of process quality, we sought an alternative test to the peer review procedure which also places a stronger emphasis on patient perspectives. The aim was to define an "ideal process" as a standard, to develop quantifiable criteria, and to test a multimethod approach which involves different data levels. On the basis of different sources, the "ideal process" for parent-child rehabilitation and prevention and associated criteria were defined by involving an accompanying expert group during a consensus process. Criteria were assessed on different levels: on the rehabilitation/prevention centre level, a questionnaire of process-relevant structural features was used; on the patient level, a case-related routine documentation filled in by clinic staff and an incident-related patient questionnaire were applied. Data were collected in 37 centres (prevention: 19; rehabilitation: 11; 7 offering both types of programmes). Analysis of patient-related data is based on a sample of 1 513 prevention patients and 286 rehabilitation patients. The resulting "ideal process" consists of the stages "preparation", "arrival", "treatment planning", "treatment", "completion of treatment", and "organisation", each containing specific criteria. Exemplarily, the outcomes for the stages "treatment planning" and "treatment" are presented. There is variability both between features and between clinics. The majority of the patients report that the criteria are fulfilled while there are medium to high levels of fulfillment regarding the routine documentation. The criteria of the questionnaire of process-relevant structural features are mostly fulfilled according to the clinics. Agreement between the 3 data levels can be observed. On the basis of the defined "ideal process", the methods that were tested seem to be appropriate to illustrate process-relevant features from different perspectives. The exemplary measured process quality of the pilot clinics can be judged as predominantly good. Individual deficits of process quality and limitations of the chosen methods are discussed.