SummaryObjectives: To compare radiography and computed tomography (CT) for the evaluation of medullary cavity diameters of metacarpal and metatarsal bones in cats and to analyse their correlation with intramedullary pin size.Methods: Radiography and CT were performed in cadavers (n = 12). The mid-diaphysis was determined and the medullary cavity diameter was measured by two observers. Each bone was osteotomized at the mid-diaphysis, Kirschner wires were inserted, and pin size was documented. Intra- and interobserver variability was evaluated (hierarchical analysis of variance). Radiography and CT were compared (correlation analysis, a t-test for dependent samples, a Bland-Altman analysis) and pin size, radiography and CT were compared (regression and correlation analysis).Results: Intra-observer variability was low for radiographs and CT, with an estimated median variation of 0.10 mm for radiographs and 0.12 mm for CT. Inter-observer variability was low, with a median variation of 0.03 mm for radiographs and 0.21 mm for CT. There was a high correlation between radiography and CT for the assessment of the medullary cavity diameter. A high correlation was found between pin size and measurement on radiographs, and between pin size and measurements on CT. In two cats, pin insertion was difficult or impossible.Clinical significance: Mid-diaphyseal measurements are applicable methods for the assessment of the medullary cavity diameter in feline metacarpal and metatarsal bones regarding intramedullary pins. In some cats the medullary cavity diameter may be too small for intramedullary pinning techniques, which can be identified preoperatively on radiographs.