In the current investigation, we used direct and indirect methods to assess and treat several topographies of aggression that were hypothesized to have separate operant functions in a young boy with severe mental retardation and pervasive developmental disorder. First, a functional analysis of aggression, using the methods described by Iwata, Dorsey, Slifer, Bauman, and Richman (1982/1994), was conducted and produced inconclusive results. Next, indirect methods were used to develop a second functional analysis, which showed that chin grinding (firmly pressing and grinding his chin against the skin and bones of others) persisted independent of social contingencies and that the other topographies of aggression (e.g., hitting, kicking) were maintained by social positive reinforcement (attention). A treatment designed to decrease aggression maintained by attention—functional communication training with extinction—reduced all forms of aggression except chin grinding. This latter topography of aggression, which we hypothesized was maintained by automatic reinforcement, was reduced when the response‐reinforcer relation was interrupted through response blocking and the child was provided with an alternative form of chin stimulation.