Difficulties in social integration pose a major mental health problem for Veterans with schizophrenia. Reviews of the literature indicate that Veterans with schizophrenia have lower marriage rates, fewer friendships, and higher rates of living alone than the general population. Poor social integration is also associated with early mortality. To gain traction on this problem, it will be necessary to find treatments that address key determinants of social integration. Evidence indicates that impairments in cognition and affect are among the key determinants of this area of functioning. Findings from the broader rehabilitation literature support a novel conceptual approach to this problem, namely engagement in physical exercise. Physical exercise is associated with improvements in attention, episodic memory, working memory, speed of processing, and executive control. In addition, physical exercise is associated with increases in positive affect and decreases in negative affect. Findings on the effects of physical exercise on cognition and affect have been reported for normal aging, mild cognitive impairment, neurodegenerative disorders, oncology, and depression, but is an area of investigation relatively new to schizophrenia. The proposed study will include 54 Veterans with schizophrenia or schizoaffective disorder (aged 45-65) who will be matched on baseline levels of cardiorespiratory fitness, and then randomized (2:1) to a walking exercise group (n=36) or a control comparison group (n=18). Veterans in the exercise group will participate in a 12-week, instructor-led, outdoor brisk walking exercise program conducted in small groups (n=6), held 3 times per week, gradually increasing walking time until reaching a maximum of 40-minutes per session. The heart rate of each Veteran will be monitored during the walking sessions to help ensure maintenance of a target peak heart rate of 60% to 70% of the maximum for the individual's age (i.e., 220-age). Veterans in the control group will participate in instructor-led, non-aerobic stretching exercises in small groups (n=6) with the duration, frequency, and total number of sessions matched to the exercise group. Primary outcome measures of cardiorespiratory fitness, cognition, and positive and negative affect of participants in both groups will be measured at baseline and the 12-week end-point assessment.