The aim of the present study was to determine the influence of method of wheat inclusion and pellet diameter on performance, nutrient utilisation, digestive tract development and carcass characteristics of broilers. The experimental design was a 3 × 2 factorial arrangement of treatments, which included three diet forms, namely ground wheat (GW) and 200 g/kg whole wheat (WW) replacing GW before or after pelleting, and two pellet diameters (3.0 and 4.76 mm). Experimental diets were offered ad libitum from Day 11 to Day 35 post-hatch. Pellet durability index was higher (P < 0.05) in GW diets and deteriorated (P < 0.05) with pre-pelleting inclusion of WW when the larger die was used. Larger pellet diameter increased (P < 0.05) the weight gain and lowered (P < 0.05) feed per gain of birds fed diets with GW and post-pellet inclusion of WW. However, in birds fed diets with pre-pelleting inclusion of WW, the larger pellet diameter lowered (P < 0.05) feed intake and weight gain, and increased (P < 0.05) feed per gain. Relative gizzard weight was increased (P < 0.05) by larger pellet diameter with pre-pelleting inclusion of WW, but was unaffected (P > 0.05) in diets containing GW or post-pellet inclusion of WW. Irrespective of the method of WW inclusion, larger pellet diameter increased (P < 0.05) the apparent metabolisable energy and ileal starch digestibility. Larger pellet diameter was associated with reductions (P < 0.05) in the relative length and weight of all components of the digestive tract in GW-fed birds, but had no effect (P > 0.05) on these parameters in birds fed WW diets. Larger pellet diameter increased (P < 0.05) carcass yield in the GW group, reduced (P < 0.05) in the pre-pelleting WW group and had no effect in the post-pelleting WW group. Overall, these results showed that the effect of pellet diameter on broiler performance varied depending on the form of wheat and method of WW inclusion. Adverse effects on weight gain in the pre-pelleting WW group were due primarily to reduced feed intake resulting from poor pellet quality.