There is evidence that patients with psychotic conditions display greater center of pressure (CoP) displacement during quite standing than healthy subjects, but the underlying impairments in the control mechanisms are uncertain. The aim of this study was to identify the nature of possible impairments in the control of posture by modulation of visual and kinesthetic information during quiet standing. Center of pressure (CoP) data and whole-body kinematics of the center of mass (CoM) were recorded during quite standing on a firm surface with eyes open and with eyes closed, and standing with eyes open on a yielding surface. During all three conditions, patients displayed greater migration of CoM and CoP-CoM, a measure related to ankle joint torque, whereas CoP-frequency (MPF) was similar in patients and healthy subjects. Our results suggested that greater postural sway in patients may depend on disproportionally large ankle joint torque without corresponding increase in frequency. Furthermore, interactions between groups and conditions suggested that the patients made less use of visual information for postural control than the healthy subjects.