In the past little attention was paid to the thoracoabdominal manifestation of Lyme radiculoneuritis, because paralysis of the abdominal wall muscles was considered to be a very uncommon clinical manifestation of Lyme neuroborreliosis. In a group of 90 patients suffering from early stage Lyme neuroborreliosis we found abdominal wall weakness in 11 cases. In the majority of patients thoracoabdominal radiculoneuritis was located in the lower thoracic segments (Th 7-12) and involved more than 3 segments (62%) mostly bilaterally (69%). Abdominal wall paralysis was mostly bilateral (91%) and involved always the lower half of the abdominal wall. It was very severe in 18%. Electromyographic studies were done in the paraspinal and abdominal wall muscles showing fibrillation potentials and positive sharp waves in 86% and 50%, respectively. Diagnosis of thoracoabdominal radiculoneuritis in Lyme neuroborreliosis may be difficult and diagnostic errors may occur. Therefore we recommend to look carefully for paralysis of the abdominal wall, which can easily be overlooked on routine neurological examination. In patients from an area with a high incidence of Lyme disease it is recommended to exclude neuroborreliosis even in patients with known diabetes mellitus in order to avoid the misdiagnosis of diabetic thoracoabdominal radiculopathy. This has occured in 2 of our patients.