Almost all investigations concerning the relationships between sibship size, sibship position and psychiatric disorders addressed more formal aspects, i.e. frequency and position, with contradictory and inconsistent results. Analyses considering sibship size and birth order as mediating factors between parental rearing and psychopathological manifestations in adults are lacking. The present results of an investigation of 1,013 psychiatric inpatients and 251 healthy volunteers support a systematic association between sibship size and parental rearing, mainly in terms of a reversed relationship between emotional warmth, overprotection and number of siblings. An excess of psychiatric patients in the middle position of a sibling seems to be related to specific unfavourable rearing patterns. A validation of our preliminary results would be required in terms of preventive measures for children of risk populations.