This article analyses interpretations of the causes of children's behavioural problems in early child psychiatry in Finland from the 1920s until the 1950s. The era was prepsychodynamic, and psychiatrists stressed biological explanations, which were based on hereditary factors. The source material consists of patient records of children diagnosed with psychopathy in Pitkäniemi Hospital, which operated as one of the state mental hospitals. The focus is on the ways in which the causes of behavioural problems were described, paying special attention to mentions of socioeconomic factors, and adopting a present-centred perspective on analysing the past. Although psychiatrists described details like family background and parental occupations, they did not necessarily use them to point out connections between socioeconomic factors and behavioural problems. On the contrary, in many cases, there was no indicated correlation. This is not to say that socioeconomic factors did not exist or were not acknowledged, but rather that they were discussed in a different light. The assumption of biologically oriented psychiatry, namely that behavioural problems were primarily hereditary, is prevalent in the case records. Some children improved while in hospital and subsequently returned home, or were placed with other families, or in children's homes. Those who were perceived to be permanently antisocial were placed in reform schools. The change in a child's behaviour seems to have been crucial in forming a prognosis, which implies that there was a clear belief in the curative atmosphere of the hospital, providing that the child's character was corrigible. The focus on socioeconomic factors contrasts with the ways in which psychiatrists at that time perceived and documented the causes of behavioural problems, and helps explain why something, which seems evident in retrospect, was not apparent at the time.