Abstracttrans,trans,anti, trans,trans-Perhydropyrene, ( 1,2,3,-3ar,4,5,5at,6,7,8,8at,9,10,10ac, lographically independent molecules in the asymmetric unit are tilted with respect to each other at a dihedral angle of 53-9" the crystal structure is of a layer type with hexagonal packing. Upon heating, a phase transformation occurs at 344.5 K which is associated with jumps of the crystals almost 6 cm high. The transformation is probably of the martensitic type with lateral shifts of lattice planes relative to each other.