The distribution of main-stem and sympodial leaves within the canopy of field-grown cotton was investigated in relation to boll development and yield. Main-stem leaves comprised a large proportion of total leaf area early in the growing season prior to boll initiation. As the season progressed sympodial leaf area increased rapidly as fruiting branches developed. Main-stem and sympodial leaves accounted for approximately 40% and 60%, respectively, of the canopy leaf area at 120 days after planting. The spatial distribution of sympodial leaves within the cotton canopy coincided with regions of the plant where maximum yield production occurred. This suggested a relationship between leaf area and yield that was especially evident from analyses of individual sympodial leaf areas and the dry weights of their subtended bolls. The implications of leaf area distribution and yield development are discussed.