Background: Compared with the general population, individuals suffering from schizophrenia are more likely to be overweight, a finding attributed to the effect of antipsychotic medications, poor nutrition, and sedentary lifestyle. As evidence accumulates indicating that some aspects of the illness manifest before the onset of psychosis and establishment of the diagnosis, it has been suggested that increased weight, like other metabolic dysfunctions, might precede active illness. Method: Data on height and weight of 203,257 male adolescents assessed by the Israeli Draft Board, and followed for 2-6 years for later hospitalization for schizophrenia using the Israeli National Psychiatric Hospitalization Case Registry, were analyzed. Results: From the entire cohort, 309 (0.15%) were later hospitalized for schizophrenia (ICD-10). After removing adolescents with evidence of illness before or within 1 year of the Draft Board assessment, 204 future schizophrenia patients were available for analysis. Compared with the rest of the cohort, future schizophrenia patients had lower body mass indexes (21.24 ± 3.3 kg/m 2 vs. 21.77 ± 3.5 kg/m 2; F = 4.682, df = 1, p = .03) and weighed slightly but significantly less (64.2 ± 11.6 kg vs. 66.3 ± 12.0 kg; F = 6.615, df = 1, p = .01). The mean height of the future patients did not differ significantly from the mean height of the remaining cohort (173.63 ± 6.7 cm vs. 174.40 ± 6.9 cm; F = 2.520, df = 1, p = .112). When reanalyzing the data, controlling for physical activity and socioeconomic status, the differences between the groups remained significant. Conclusion: Before the onset of illness, future schizophrenia patients are not heavier compared with their peers. This implies that the increased weight of patients with schizophrenia is related to illness effects, including the effects of antipsychotic medication.