A prospective hospital-based multicentre study in Lower Saxony allowed to investigate the frequency of acute peripheral facial palsy due to Lyme borreliosis and its clinical and laboratory characteristics. Diagnosis of Lyme Borreliosis was based on detection of IgM antibodies against Borrelia burgdorferi in serum and CSF as well, using an IgM capture ELISA. Between June 1986 and October 1987 27 consecutive cases with acute peripheral facial palsy were studied. Lyme borreliosis is the main cause of peripheral facial palsy in childhood. It was verified serologically in two thirds of the cases. All cases with a positive history for a tick bite and/or an erythema migrans in the head-neck region showed ipsilateral neurological affection suggesting a direct invasion via the affected nerve by Borrelia burgdorferi. Peripheral facial palsy due to Lyme borreliosis represents a monosymptomatic meningoradiculitis. All children with Lyme borreliosis revealed a lymphocytic CSF pleocytosis, whereas in cases of unknown etiology CSF findings usually were normal. Therefore, in any case of facial palsy with an inflammatory CSF syndrome Lyme borreliosis has to be suspected unless proven otherwise.