The data challenge the conventional view that a disproportionate number of prisoners exhibit symptoms of psychological and psychiatric disorders because they are mentally ill before they enter jail. The SCL-90 was administered to 339 prisoners within 72 hours of confinement; respondents were asked to rate symptoms since they had been confined the week prior to their arrest and confinement. The instrument was administered again to available members of the sample (102) after 5 days of incarceration. Analysis of prisoner symptom scores for the three rating intervals indicated that, for several dimensions, symptoms increase markedly during the initial period of incarceration and then stabilize or diminish after 5 days of confinement. The findings demonstrate that jail can have considerable effects on symptom levels, and these effects are not restricted to those normally viewed as susceptible. Results suggest that those who hold an exclusively person-centered view of psychological disturbance among jail prisoners should expand their view to include the contribution of the jail environment. Data tables, notes, and 18 references. (Publisher abstract modified)