A 4‐year‐old, female, neutered Labrador Retriever was referred with tail flaccidity of acute onset after an extensive period of swimming. There were no other neuromuscular clinical signs on physical examination and no pain of tail palpation. Comorbidity was reported, with previous diagnosis of hypothyroidism (9 months before), but the disease was considered controlled since levothyroxine supplementation. Despite the impossibility to confirm nonrelated neuromuscular impairment associated with hypothyroidism, the fast resolution of clinical signs without intervention was more likely to confirm a limber tail syndrome rather than an endocrine neuromyopathy, but, to the authors' knowledge, this is the first report of its kind, and further investigations are required.