A 24-day-old female newborn presented with multiple annular erythematous plaques with a targetoid shape, on the forehead, neck and upper trunk, that had begun ten days earlier. She had been diagnosed with citrullinemia type 1 in the first week of life and arginine supplementation was initiated. Her personal and family history was otherwise unremarkable. Laboratory tests showed high levels of anti-La/SSB and anti-Ro/SSA in both mother and baby. The patient was diagnosed with Neonatal lupus erythematosus on the basis of the clinical, histopathological and laboratorial findings. Neonatal lupus is a rare immune-mediated disease that results from transplacental transfer of maternal IgG antinuclear antibodies. The disease can affect different organs, mainly the skin and heart. Although the skin lesions are usually characteristic, they pose a diagnostic challenge in the absence of maternal history.