No, inflammatory bowel disease (IBD) is not thought to be contagious. The cause of IBD is unknown, but it is thought to have both a genetic and an environmental component. IBD runs in families, but it tends to be more complicated than just being passed from parent to child. If the genetic piece is in place, the environmental component -- and no one knows exactly what that is -- may work as the trigger to set off the IBD.
A study was done in Belgium in the 90s that investigated married couples who both developed IBD. The researchers thought that because these couples developed IBD after marriage, that IBD must be contagious. The 10 examples cited in the study are thought to be rare. In fact, this occurrence is so rare, it is actually an argument against the idea that IBD can be contagious.
M C Comes, C Gower-Rousseau, J F Colombel, J Belaïche, H J Van Kruiningen, M C Nuttens, and A Cortot. "Inflammatory bowel disease in married couples: 10 cases in Nord Pas de Calais region of France and Liège county of Belgium." Gut Sept 1994 35:1316–1318. 24 Apr 2008.
Laharie D, Debeugny S, Peeters M, Van Gossum A, Gower-Rousseau C, Bélaïche J, Fiasse R, Dupas JL, Lerebours E, Piotte S, Cortot A, Vermeire S, Grandbastien B, Colombel JF. "Inflammatory bowel disease in spouses and their offspring." Gastroenterology Mar 2001 120:816-819. 24 Apr 2008.