The 147-nm photolysis of SnH4 results in the formation of H-2, Sn(s), and a very small amount of Sn2H6. The quantum yields decrease with increasing partial pressure of SnH4, at 0.2 Torr being Phi(-SnH4) = 5.6 +/- 0.3, Phi(H-2) = 11.4 +/- 0.6, and Phi(Sn2H6) = 0.059 +/- 0.02. A mechanism is proposed that is shown to be internally consistent and in agreement with the experimental facts.