During Drosophila embryogenesis, Smaug protein represses translation of Nanos. through an interaction with a specific element in its 3'UTR. The repression occurs in the bulk cytoplasm of the embryo; Nanos is, however, successfully translated in the specialized cytoplasm of the posterior pole. This generates a gradient of Nanos emanating from the posterior pole that is essential for organizing proper abdominal segmentation. To understand the structural basis of RNA binding and translational control, we have crystallized a domain of Drosophila Smaug that binds RNA. The crystals belong to the space group R3 with unit cell dimensions of a = b = 129.3 Angstrom, c = 33.1 Angstrom, alpha = beta = 90degrees, gamma = 120degrees and diffract to 1.80 Angstrom with synchrotron radiation. Initial characterization of this domain suggests that it encodes a novel RNA-binding motif.