Disclosed is a novel polymorphic form of the compound of formula (I) also known as mutilin 14-(exo-8-methyl-8-azabicyclo[3.2.1]oct-3-ylsulfanyl)-acetate, a process for the preparation of the polymorphic form, pharmaceutical compositions comprising the polymorphic form, and the use of the polymorphic form in medicine, particularly in antibacterial therapy.