Here we describe the first skeletal evidence of a tetrapod from Rhaetian (Upper Triassic) marine deposits of the Western Carpathians. The material consists of an isolated left femur and comes from the Úbočka locality near Čičmany in the Strážov Highlands. Based on morphological, histological, and stratigraphic evidence, we can exclude affinities of this femur to the most commonly occurring aquatic reptiles: the Eosauropterygia. The histology of a femur of aff. Pachystropheus from Aust Cliff, Gloucestershire, UK, is also described here for the first time and compared to the bone from Slovakia. However, a precise taxonomical assignment of the Rhaetian femur from Slovakia is not possible. The bone shows strong osteosclerosis that points to an inhabitant of a shallow marine environment. On the basis of morphological and histological characters, affinities to a cyamodontoid placodont, Endennasaurus-like thalattosaur or a rhynchocephalian are conceivable. The morphology of the Slovak find does not fully exclude choristoderan affinity, but the rare histological data available for comparison do not support such a statement. For all these reasons, we allocated this bone as Diapsida indet. The bone described here sheds the first, although limited light on the possible faunal composition of the Rhaetian tetrapod assemblage in the Western Carpathians. We can assume that the bone, which shows marks of transport, either represents an allochthonous component in this marine environment, transported postmortem and most likely from nearby dry land (i.e., in the case of rhynchocephalian affinities), or it belonged to an inhabitant of this shallow coastal biotope (e.g., cyamodontoid placodont affinities).