Received 20 June 2015; revised 6 August 2015; accepted for publication 7 August 2015Optimality theory suggests that parasitic cuckoos should evolve an optimal laying behaviour aiming to positivelyselect host nests in which the eggs match the phenotype of their own eggs, thus minimizing the rejection riskfrom hosts and, in turn, maximizing the cuckoos’ fitness. We tested this hypothesis by investigating cuckoo-eggmatching between parasitized and nonparasitized nests in a common cuckoo (Cuculus canorus) host, the Orientalreed warbler (Acrocephalus orientalis), by use of Vorobyev–Osorio and Nature-Pattern-Match models to quantifythe matching of egg colour and pattern from avian vision, respectively. The results of our study indicated thatcuckoo-egg matching in parasitized nests was no better than that in nonparasitized nests, and thus we found nosupport for the optimal laying hypothesis in cuckoos. The mixed conclusions from all previous studies, includingthe present study, may be explained by (1) the parallel coevolution in different cuckoo–host systems; (2) theinappropriate methodology; and (3) the deficiency of the assumption itself. We suggest that a better methodologyshould be developed to solve the puzzle of whether cuckoos choose to lay eggs matching those of the host. © 2015The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 00, 000–000.