Seed rot was first observed in cotton fields in Hampton County, SC, during the last week of July 1999. Growers and crop consultants monitoring insect feeding and boll maturity detected poorly developed and discolored,“rotting” seed in bolls of several varieties. “Seed rot” was observed in apparently healthy fields which had high yield potentials 3 to 4 weeks after the initiation of flowering. Bolls containing seed rot exhibited no outward symptoms of seed rot or any other problem. Symptoms were most visible when bolls were cut open transversely. Affected seed were poorly developed and often hollow, while less affected seed were pinkish in color and partially hollow. Some seeds exhibited thickening or uneven development of the seed coat. Bolls in which seed rot occurred did not mature normally and often were hard-locked, i.e. unharvestable with a mechanical picker. Significant yield losses occurred where the incidence of seed rot was high. Fields with boll exhibiting “seed rot” symptoms were reported in North Carolina, South Carolina, Georgia, Florida, Alabama, and the Coastal Bend region of Texas in 2000. South Carolina survey data detected seed rot in all 23 cotton producing counties examined in South Carolina in 1999 and 2000. Seed rot was found in all 45 varieties examined. Seed rot was detected in conventional varieties and varieties with either the Bromoxynil, Boll Guard and/or Roundup Ready genes. No correlations between the occurrence of either supernumerary carpels or insect feeding and the presence of seed rot was noted. No specific weather event or pattern was tightly linked to the occurrence of seed rot. The possibility that poor development of the seed was due to incomplete pollination and/or fertilization was also examined.