This case-control study investigates etiologically important factors for juvenile osteosarcomas and possible reasons for the relative scarcity of their incidence in the population. Information on a variety of risk factors, psychosocial factors, and factors possibly occurring in early childhood was obtained by interviewing 88 patients (ages 8-25 years) with osteosarcoma, Ewing's sarcomas and other bone tumors, and three age- and sex-matched control groups (hospital, neighbour and family controls), and their mothers. For both sexes, children's diseases in their history, which increased the risk were measles (RR = 1.56, not significant) and mumps (RR = 1.81, 95% CI = 1.05-3.13), whereas clinically apparent chickenpox was associated with a significant decrease for bone tumors (RR = 0.46, 95% CI = 0.26-0.8). Dermal and respiratory allergies (without hay fever) were also inversely associated with bone tumors. Breast feeding for longer than 2 months was associated with low risk for bone tumors for boys, whereas for girls, paternal age was a risk factor; remaining stable in a multivariate model (RR = 2.36, 95% CI = 0.90-6.21). A change in the presence of an emotionally significant person or changes of residence were risk factors both in univariate and multivariate analyses. The strongest and most persistent risk factor was difficulties in school, indicative of emotional disturbances (RR = 2.58, 95% CI = 1.39-4.78). Considering such host factors as possibly important modifiers of risk in addition to exogenous carcinogenic agents, these factors were consistent and statistically significant for both sexes and despite the small numbers recruited for this study, thus predicting susceptibility. The factors may become relevant for preventive psychotherapy applied to susceptible persons for improvement of prognosis after surgical therapy in preventing recurrences.