A retrospective evaluation of 17 dogs treated surgically for idiopathic acquired laryngeal paralysis demonstrated a marked variability in outcome, with many dogs continuing to exhibit weakness and exercise tolerance. In a subsequent prospective study, 22 consecutive affected dogs were tested for neurological deficits by neurological examination, electrodiagnostic evaluation, and blood analysis to measure thyroxine and thyroid-stimulating hormone and to detect any evidence of myasthenia gravis. Clinical neurological deficits and/or electrodiagnostic abnormalities were found in each case. There was limited evidence that specific neurological deficits were associated with a poor prognosis for full recovery of exercise tolerance. None of the dogs was positive for anti-acetylcholine receptor antibodies, and only three showed evidence of thyroid dysfunction.