Improvement of seedling vigor in cotton (Gossypium hirsutum L.), depends on defining and evaluating specific seedling traits. The objectives of this study were to evaluate relationships among and inheritance of seedling traits that may be associated with seedling vigor. Seedlings of six cultivars and their 15 F₁ progenies from a diallel mating were grown for 14 days in controlled environmental conditions. Seeds were pre-germinated to lessen possible seed quality and emergence differences. The presence or absence of the herbicide trifluralin [2,6-dinitro-N,N-dipropyl-4-trifluorometil) benzenamine] was used to establish conditions for good and poor seedling development, respectively. Number of lateral roots, seedling height, and fresh and dry weights were reduced by the trifluralin treatment, but not significantly affected by genotype-by-treatment interactions. Each seedling parameter tended to be positively correlated with high values for the other seedling parameters, with the exception that number of lateral roots was independent of seedling height. General combining ability was the major source of genetic variation for each trait while specific combining ability was significant only for fresh weight of seedlings. Number of lateral roots and seedling height should respond to direct, nondestructive selection in early generations.