In Tanzania, cotton is of great economical importance, representing a large percentage of agricultural exports, but yield and lint quality is still relatively poor. The aim of this study was to identify parents to improve boll and lint yield and quality. Parents and F1 progeny of a 7 × 7 diallel were evaluated in four different environments. Results indicated significant variation for especially yield components, yield, ginning outturn and fibre quality. Parents with high and positive GCA like NTA 93-21, Delcot 344, Auburn 56 and MZ561 and combinations with high and positive SCA for the characteristics were identified. Additive genetic effects were seen for most of the characteristics, except for fibre strength at one locality. Parents with high GCA effects for certain characteristics produced combinations with high SCA effects for the same characteristics. This study indicated that there is enough genetic variability for boll and lint yield and quality for effective selection, and good parents that can be included in the breeding programme.