To assess the influence of a 50% distal ulnectomy on mediolateral carpal stability in the dog.Canine cadaveric study.Seven canine thoracic limbs METHODS: Thoracic limbs were placed in a jig to mimic weight bearing with a load representing 30% of body weight. Carpal extension angle was standardized at 190° ± 5°. Frontal plane carpal angles were measured with the limb loaded on craniocaudal radiographs before and after ulnectomy. Valgus and varus stress radiographs with the limb loaded were acquired before and after ulnectomy. The limbs were palpated and were subjectively graded for valgus or varus instability by 2 investigators before and after ulnectomy.Mean (±SD) valgus angulation increased after ulnectomy (2.1° ± 1.7°; P = .017; CI95 = 0.5°-3.7°) when the limb was loaded without valgus or varus stress applied. Mean valgus angulation increased after ulnectomy (2.7° ± 2.8°; P = .032; CI95 = -0.2°-5.5°) when valgus stress was applied to the loaded limb. Varus angulation was unchanged after ulnectomy (0.6° ± 4.6°; P = .383; CI95 = -4.2°-5.3°) when varus stress was applied to the loaded limb. Palpation detected increased valgus score after ulnectomy.Distal ulnectomy with excision of the lateral styloid process induces a slight increase in valgus in canine cadaver carpi. The clinical consequences of that valgus on carpal function and health should be assessed in clinical patients.