We examined the relation between sleep deprivation and changes in level and allocation of aberrant behavior (aggression and self-injury) for a child with moderate mental retardation. First, a series of functional analyses identified that self-injury (SIB) and aggression were maintained by escape from demands (i.e., were members of the same response class). Escape from demand conditions were then held constant over time while natural levels of sleep deprivation occurred. This final analysis demonstrated a correlation between sleep deprivation and increases in escape-maintained aberrant behavior. Sleep deprivation seemed to be related to increases in levels of self-injury but did not seem to influence levels of aggression.