Genetic control of stem diameter and other stem attributes of wheat in relation to yield components were analyzed in a 7- parent F1 diallel cross in favorable, drought and drought combined heat environments, as well as in 12 F2 populations under heat stress. Polygenes with mainly additive effects were involved in the control of stem diameter which segregated in normal distributions in the F2. The narrow-sense heritability was of comparable magnitude under favorable (0.73), drought (0.62) and drought + heat stress (0.76); whereas heritability of stem dry weight was reduced under stress. Stem diameter was positively correlated under both drought and drought + heat stresses with stem weight and stem density. Stem diameter was significantly associated with 1000 kernel weight and grain yield per spike in three environments. Such strong associations of stem diameter with single grain mass and grain yield per spike under stress indicated the important role this character play in sustaining grain filling through provision of greater capacity for assimilation in the stem before mobilizing it to grains.