The antiretroviral agent tenofovir can cause hypophosphatemic osteomalacia due to renal phosphate wasting. The potential role for Fibroblast Growth Factor 23 (FGF23), a phosphaturic hormone is unknown. We evaluated FGF23 plasma concentrations in an HIV-positive patient with neurofibromatosis in whom hypophosphatemia developed during tenofovir therapy. This patient presented with diffuse pain, hypophosphatemia and tubular dysfunction with inadequate phosphate reabsorption. The full recovery after tenofovir discontinuation indicates that the hypophosphatemia was related to tenofovir and not to von Recklinghausen disease. Our data argue against a role for FGF23 in tenofovir-induced hypophosphatemia nor in the regulation of hypophosphatemia in this situation.