Eighteen new plagioclase  ⁴⁰Ar/³⁹Ar and 7 whole rock K/Ar ages from magmatic dykes in the South Shetland Islands (Antarctic Peninsula) suggest they are Paleocene to Eocene in age. Intrusion began earlier and lasted longer on Hurd Peninsula (Livingston Island) than on King George Island and probably also Nelson Island. The oldest dykes from Hurd Peninsula did not yield ⁴⁰Ar/³⁹Ar plateau ages, but best estimates indicate intrusion at about the Cretaceous/Paleogene boundary, probably Danian. A Campanian age of the host and the inferred Early Danian age for the oldest dykes leaves a time gap of 5-10 m.y. for the deformation of the metasedimentary host. The main phase of dyke intrusion in the South Shetland Islands took place from Thanetian to Lutetian, culminating between 47 and 45 Ma and terminating during the Priabonian, with the youngest dykes restricted to Hurd Peninsula.