Microsporum praecox Rivalier ex Padhye, Ajello et McGinnis is the validated name for the taxon originally published as Sabouraudites praecox Rivalier. We describe here the first case of small-conidial, ectothrix type hair invasion caused by M. praecox in an adult woman from Oklahoma, U.S.A., suffering from sickle cell anaemia. This fungus is now being encountered with greater frequency as an etiologic agent of ringworm infection.