Traditional interview studies of inconsistent parental discipline show a strong link with young children's conduct problems. Observational studies of inconsistency show weaker links with problem behavior and suffer from methodological problems. This study proposed a new observational definition of parental inconsistency, which analyzed whether mothers follow through their demands during sequences of mother-child conflict. A home observational study showed that mothers of conduct-problem preschoolers acted inconsistently during a greater proportion of conflict episodes than did their normal counterparts. There was a strong correlation between inconsistency and amount of family conflict. Inconsistency varied as a function of the context from which conflict arose. Results are discussed in terms of both coercion (Patterson, 1979) and predictability theories of problem behavior (Wahler & Dumas, 1986).