Benzoxa- and benzthiazoles substituted at the 2 position and carrying a sulfamic acid ester group bound via oxygen to the phenyl part of the ring structure, such as the compounds of formula (I) wherein the symbols have various significances, possess interesting pharmacological activity. They can be prepared by sulfamoylation of a corresponding compound carrying a hydroxy group on the phenyl part of the ring structure, or by N-substitution. They are indicated for use as steroid sulfatase inhibitors in the prevention and treatment of illnesses responsive to steroid sulfatase inhibition, such as acne.