Research into the effects of environmental deprivation on negative symptoms of schizophrenia is limited, and few attempts have been made to differentiate secondary symptoms caused by the social environment. Japan's mental health system allows us to examine the extent to which understimulating social environments in hospitals contribute to negative symptoms of institutionalized patients while controlling for other factors. A random sample of inpatients of diagnosed with schizophrenia and hospitalized for 1 year or longer was drawn from the universe of inpatients attending a convenience sample of 20 hospitals across Japan. Data were collected for 549 study participants (a response rate of 91.5%). Measures included the Scale for the Assessment of Negative Symptoms (SANS), other clinical condition scales such as the Manchester Scale, and social condition scales including the Nurses' Opinion Scale and the Ward Restrictiveness Scale. Hierarchical regression analyses were conducted to determine the contribution of social environment to negative symptoms. Results showed significant correlations between negative symptom scales and most of the social environment scales, where social environment scales accounted for 18% of the variance in SANS scores. The study confirms the influence of understimulating social environments in psychiatric hospitals on negative symptoms.