This article reveals the reason for specific way of competition law enforcement in markets defined within the context of interrelation between the main and derivative products. Identifying particularities of grounds for aftermarkets definition we provide systematization of various types of interrelations between main product and derivative product taking into account possible cases for two related markets and single one in product boundaries; competition and monopolization of single market, both markets or one of them. The set of competition restrictions problems within the «main product - derivative (supplementary) product» relationship is defined on the basis of studies in the New Institutional Economic theory taking into account the contracting between producers (sellers) and buyers of products mentioned. It is explained significance of such aspects of interrelations between buyers and sellers of complex durable goods as fundamental transformation, switching cost, hold up, contracts incompleteness. Based on lessons learned from «Kodak» and some other cases the issue of limits for efficient antitrust enforcement is discussed. The problem of excessive antitrust enforcement as an substitute of contracts design by private actors demonstrate the risk of crowding out of private ordering of contracts by public ones. The article shows some signs of specific vector of Russian antimonopoly law enforcement related to aftermarkets issues. It is discussed particular case of product boundaries definition of market (stripes for tests to check quantity of sugar in blood) and wider classification of interrelations between the main and derivative products taking into account not only individual market dominance but also collective market dominance.