Abstract Fusarium wilt is caused by two closely-related fungi, Fusarium oxysporum f. sp. vasinfectum and Fusarium oxysporum f. sp. cannabis. The disease was first described on hemp in Eastern Europe about 50 years ago, but is now found throughout the Northern hemisphere. Greenhouse studies demonstrated that all cultivars of Cannabis that were tested are susceptible. Signs and symptoms, life history of the pathogens, and control measures are discussed. Fusarium wilt is a menace to hemp cultivation worldwide because its causal fungi cannot be constrained by known organic control measures. The disease threat is compounded by misguided attempts to spread the fungi around the world to stop illicit marijuana cultivation.