The porcine adenovirus NADC-1 isolate, a strain of porcine adenovirus type 4, has a fibre with an atypical architecture. In addition to a classical virus-attachment region, shaft and head domains, it contains an additional galectin-like domain C - terminal to the head domain and connected to the head domain by a long RGD-containing loop. The galectin-like domain contains two putative carbohydrate-recognition domains. The head and galectin-like domains have been independently crystallized. Diffraction data have been obtained to 3.2 Å resolution from crystals of the head domain and to 1.9 Å resolution from galectin-like domain crystals. © 2009 International Union of Crystallography. All rights reserved.