Several neurological manifestations of Lyme disease, both central and peripheral, have been described. Reported here is a case of acute transverse myelitis related to a Lyme neuroborreliosis that presented with isolated acute urinary retention and no lower-extremity impairment. This case, documented by urodynamic and electrophysiological investigations, partially resolved after 6 weeks of intravenous ceftriaxone, affording the removal of the indwelling catheter. Alpha blocker therapy was needed for 3 months, until the complete normalisation of urodynamic and electrophysiological records. This case study indicates that whenever urinary retention is encountered associated with acute transverse myelitis or alone, the patient should be investigated for Lyme disease.