A case of acute generalised exanthematous pustulosis (AGEP) after cefotaxime use confirmed by a positive patch test is reported. A 30-year-old woman received cefotaxime, fosfomycin and ciprofloxacin for sinusitis. At 12 days after drug initiation, she developed an extending pustular erythaema associated with fever. Laboratory investigations showed marked leukocytosis. Her blood chemistry was normal. The histological examination showed parakeratosis, spongiosis and non-follicular intra epidermal pustules consistent with AGEP. All medications were withdrawn. The symptoms resolved within 11 days after cefotaxime discontinuation. Patch tests were positive to cefotaxime after 48 h, while ciprofloxacin and fosfomycin yielded negative findings. Based on the Naranjo algorithm, it is probable that the AGEP reaction was due to cefotaxime. To our knowledge, this is the first reported case of AGEP associated to positive cefotaxime patch testing.