This case report highlights the diagnostic challenge that herpes zoster represents if pain develops in the prodromal stage. A 58-year-old male presented with pain in the left maxilla. The symptoms had lasted for 7 months. The first premolar had been extracted soon after the onset, and the second premolar root filled shortly thereafter. Symptoms were experienced as sudden pain attacks lasting for several hours and analgesics gave some pain relief. Clinical examination showed that the second premolar was tender to percussion. No sinus tract or swelling were present. Radiographic examination showed previously root-filled second premolar and first molar teeth, and no evidence of apical pathosis. Due to the uncertainty about the quality of the root filling in the second premolar and incomplete root filling in the first molar, retreatment was started prior to prosthetic treatment in the region. The pain continued and became more intense during the treatment. A diagnosis of herpes zoster was determined, when an acute attack with oedema and vesicles occurred, 2 months after retreatment was started. In the present case, therefore, the primary attack presented itself after months and the herpes zoster diagnosis could not be made until then. points. Key learning points. * A long lasting prodromal stage is an unusual event. * Symptoms combined with inadequate technical standard of root fillings may confuse the diagnostics. * No available data support or suggest the use of antiviral treatment as a diagnostic tool.