In recent years, many states have legalized marijuana for medical use, recreational use, or both. At the same time, parental drug abuse is now the second most frequent reason for a child's placement into the foster care system (34 percent of all entries in 2019). We investigate the causal link between these two facts. Do states that legalize marijuana experience an increase in foster care entries related to drug abuse? We utilize multiple difference-in-difference approaches to exploit the state level variation in recreational and medical marijuana laws. Our findings suggest that when states permitted recreational marijuana use, there was no corresponding change in the number of foster care entries related to drug abuse, relative to control states. For the legalization of medical marijuana, we find an 8-10 percent decrease in the number of cases associated with parental drug abuse in the first two years, followed by an 18 percent decrease in the third year. We calculate that on average, approximately 700 fewer entries to foster care related to parental drug abuse occurred when a state legalized medical marijuana.