A 46-year-old woman was admitted to our department with symptoms of nausea, anorexia and asthenia. Serum alanine aminotransferase and aspartate aminotransferase levels were increased; all serological tests for viral hepatitis and autoimmune disorders were negative. She had taken Lycopodium similiaplex solution as sedative for the previous 8 weeks, whose two constituents, Lycopodium serratum and Chelidonium majus, are found to be potentially toxic. After discontinuing L. similiaplex use, liver values returned to normal and she was asymptomatic. The diagnosis was definitively confirmed by liver biopsy; on the basis of the histological specimen, a hypersensitivity reaction was hypothesized as a possible pathogenic mechanism. Hepatotoxicity of phytotherapy has already been described, although so far, the true incidence and the pathogenic mechanisms are largely unknown. It is important to increase awareness of both clinicians and patients about the potential dangers of herbal remedies; surveillance systems and quality control of these products are necessary.