The ultraviolet spectrum of methyl isothiocyanate (CH3NCS) and the quantum yield for its dissociation into methyl isocyanide (CH3NC) and atomic sulfur at 308 nanometers, PHI = 0.98 +/- 0.24, were measured. Methyl isothiocyanate is widely used as an agricultural fumigant and readily enters the atmosphere during and after application. The results indicate that photodissociation by sunlight is an effective pathway for its removal from the atmosphere.