The stone itself is substantial, measuring 1.3 metres long and 0.9 metres wide, and its surface carries sixteen cup marks, with traces of a seventeenth where a corner of the boulder appears to have broken away at some point. Cup marks are among the most common forms of prehistoric rock art found in Ireland: simple hemispherical hollows ground or pecked into stone, their precise purpose still debated. What makes this boulder more elaborate than most is that four of the largest cups, measuring 10 to 12 centimetres across and roughly 6 centimetres deep, are each enclosed within incised circles, giving them the distinctive cup-and-circle form that recurs across Atlantic Europe during the Neolithic and Bronze Age periods. One cup has only a semicircle rather than a full ring around it. Three incised linear grooves also run across the surface, adding to the sense that the decoration was deliberate and varied rather than casual.

The stone was first formally recorded on 29 January 1933, when a researcher named Price described, photographed, and drew it. Price also noted at the time that three other marked stones lay nearby: a flat flag with small cups roughly a hundred yards to the south-east, a granite boulder with six or more small pits to the east, and a mica schist flag covered in pits about two hundred yards to the south. None of those three stones has since been located, according to research published by Corlett in 2005. Their disappearance, whether through agricultural disturbance, burial, or simple mislaying in the landscape, leaves the Baltynanima boulder as the only survivor of what appears to have been a small cluster of decorated stones. The Wicklow Rock Art Project, based at the School of Archaeology in University College Dublin and directed by Dr Clíodhna Ní Lionáin, has produced a photogrammetric three-dimensional model of the stone, allowing the carved surface to be examined in detail without needing physical access to its current garden setting.