Cotton aphid, Aphid qossypii Glover, caused significant yield reductions in cotton test plots grown at Stoneville, MS in 1990 and 1991. The period of highest infestation levels was in mid season, late June through late July, in both years with the infestation peak about mid July, when cotton in the Midsouth usually reaches peak bloom and boll set. Regression analysis of aphid infestation, expressed as accumulated "aphid days" per leaf, against seed cotton yield showed a significant negative relationship. These studies closely agree with results reported earlier by Andrews and Kitten (1989). Quality measures of lint samples from the 1990 tests showed no effect on lint quality or "stickiness" by the relatively high midseason cotton aphid infestation. Simple economic analysis of projected lint and seed loss indicates that returns to cotton aphid control exceed cost fairly quickly with increased aphid day accumulations.