Electronic cigarettes (e-cigs), any health risks?
Since the question is about risk specific to e-cigarette as opposed to classic cigarettes, what's left is the potential harm from the chemicals in refill-fluids (apart from nicotine): polyethylene glycol, glycerol, alcohol, linalol, flavours. You can find cytotoxicity experiments (e.g. http://www.sciencedirect.com/science/article/pii/S0890623812002833), that show that the most harmful components may be the flavouring compounds. Some other articles (I can't find a reference right now) point out that the moderate heating of the fluid might create harmful byproducts, differently from those in regular cigarette: acroleine, formaldehyde. The use of e-cigarette is probably too recent to have long-term studies that answer your question.