Growth of perylene crystals by vapor phase deposition on a liquid substrate is observed by video microscopy. For a range of perylene molecule concentrations in the oil film a regime of unidirectional needle crystal growth is discovered. For even higher concentrations a switch in the preferential growth direction is found. Both growth anisotropies are linked to the loss of inversion symmetry in the growth environment, causing unidirectional anisotropies in the growth kinetics. Similar anisotropies can be expected for organic thin film growth on solid substrates. (C) 2004 Elsevier B.V. All rights reserved.