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Due to the intensification of dairy herds and the recognition of subclinical infections with a negative impact on production as disease, control of gastrointestinal (GI) nematodes in adult cows is becoming established in an increasing number of dairy herds. The objectives of this paper are to review the aspects related to the impact on production, diagnosis and control of GI nematodes in adult dairy cattle. During the last decade substantial evidence has been generated that GI nematodes can have a negative impact on the performance of adult animals. The milk-yield response to anthelmintic treatment in recent studies in pastured dairy herds was observed to be around 1kg/cow per day, whereas effects on reproductive performance remain equivocal. GI-nematode infections can be monitored based on Ostertagia ostertagi-specific antibody measurement, which provides information on the level of larval exposure and an indication of the associated production losses. Other diagnostic parameters are considered of limited use in adult cattle. Control relies on anthelmintic treatment and grazing management, which can be used complementary to each other. There are three critical points that need to be considered when developing anthelmintic control recommendations in adult cows: the unpredictability of the treatment response, the timing of treatment and the risk for developing anthelmintic resistance. As a consequence, monitoring of GI-nematode infections is desirable in order to focus anthelmintic treatments on those herds with a high larval challenge and associated production losses. For the future, more studies are needed to evaluate the effects of different control approaches in terms of financial benefits for the farmer and sustainability on the long term.