From gas phase reactivity studies employing tandem mass spectrometry, the unimolecular dissociation of the corresponding base of glycolaldehyde has been probed under conditions of collisional activation. Three reactions were observed (in order of decreasing abundance): loss of CO, CH2O, and loss of H-2. Detailed reaction mechanisms for each of the three reactions were obtained by quantum chemical calculations, and the reaction characteristics and energetics were found to be in good agreement with experimental observations. The relevance of these findings to the formose reaction and possible interstellar formation of carbohydrates from formaldehyde is discussed. It is concluded that the critical C-C bond forming reaction between two formaldehyde molecules to give the glycoladehyde is unlikely to occur in the gas phase via a route involving the free formyl anion, thereby precluding a key pathway for interstellar formation of carbohydrates. However, an alternative formation reaction is suggested.