The brown marmorated stink bug, Halyomorpha halys (Stål, 1855) (Hemiptera: Heteroptera: Pentatomidae), has been spreading over Europe since the first documented records from Liechtenstein in 2004 and Switzerland in 2007. It is considered to be a pest in many agricultural crops and a household nuisance. In 2017 the species was observed in Croatia for the first time, in the city of Rijeka on the north Adriatic coast. Halyomorpha halys has already been recorded in three nearby countries (Italy, Hungary and Serbia), and therefore the arrival of this species had been expected from neighbouring populations or from distant sources via trading goods. To identify the pathway of entry, the haplotypes of H. halys (Stål, 1855) individuals were analysed by comparing a part of the mitochondrial COI gene with other haplotypes present in the GenBank database. Individual specimens shared the most common haplotype with nearby Italian and Hungarian populations.