The aim of the present study was to investigate the effect of varying levels of whole-grain wheat in the diet (12.5%, 25%, 37.5% and 50%) on the particle size spectra of duodenal digesta and nutrient digestibility in young turkeys. After feeding from 4 to 8 weeks of age, a linear increase in particles larger than 2 mm (P = 0.002) and a linear decrease in particles ranging in size from 1 to 2 mm and smaller than 0.071 mm (P = 0.001; excluding particles ranging in size from 0.106 to 0.071 mm) were noted in the duodenal digesta of turkeys. No differences were observed in the digestibility coefficients of dry matter and crude fibre or in nitrogen retention. Our findings indicate that the inclusion of whole wheat in the diet increased the proportion of coarse particles in the digesta leaving the gizzard, which did not reduce the apparent digestibility of dry matter and crude fibre, or nitrogen retention. Nonetheless, both the weight gain and feed conversion ratio worsened linearly with increasing amounts of whole wheat in the diet (linear contrast P = 0.002 and P = 0.001, respectively).