The possible effects of solitary confinement on prisoners' health were studied using a prospective design. 27 secluded prisoners were compared with 27 others who were held in custody. The latter group of prisoners was able to see other prisoners, visitors, friends and family members, and could participate in prison activities. The results showed that secluded prisoners had more health problems than prisoners serving less restrictive prison sentences did. The most usual complaints were headache, pain in the neck, stomach and shoulders, anxiety and depression. Psychotic symptoms were rare. The complaints tended to last for the whole period of solitary confinement and were difficult to treat while the prisoners remained secluded. Patients with chronic somatic diseases tended to deteriorate in solitary confinement. Most patients recovered when the seclusion was terminated.