Four new diatom species belonging to the genera Achnanthidium, Placoneis, Geissleria and Stauroneis were observed during a survey of the non-marine diatom flora of several islands in the Maritime Antarctica and South Georgia. Based on light- and scanning electron microscopical observations, the following species are described as new: Achnanthidium lailae Van de Vijver sp. nov., Placoneis australis Van de Vijver et Zidarova sp. nov., Geissleria gabrielae Van de Vijver et Zidarova sp. nov. and Stauroneis nikolayi Zidarova sp. nov. The new species are compared to other morphologically similar species from Europe, South America and the (sub-)Antarctic region. Data on their ecology and biogeography are also given.