The study was conducted to evaluate whether Bemisia tabaci (Gennadius) (MEAM1, formerly B biotype) populations in Turkey have developed resistance to neonicotinoid insecticides. We collected B. tabaci from vegetable and cotton growing areas in the Mediterranean coastal region of Turkey. B. tabaci populations were collected from the following crops (and areas): Solanum lycopersicum L. (Aydmcik and Erdemli-Mersin), Gossypium hirsutum L. (Karatas-Adana), Capsicum annuum L. (Kumluca-Antalya), and Cucumis sativus L. (Samandag-Hatay). We performed insecticide bioassays and biochemical assays to determine levels of susceptibility to acetamiprid, imidacloprid, thiacloprid, and thiamethoxam. The bioassays showed that most of the B. tabaci populations were resistant to all the neonicotinoids tested when compared with the laboratory insecticide-susceptible strain, SUD-S. The highest resistance factor was 2060 for imidacloprid at Kumluca and the lowest was 5.36 for thiamethoxam at Samandag. Furthermore, the highest and lowest monooxygenase enzyme activity level of B. tabaci was in the Kumluca and Samandag populations, respectively. The CYP6CM1 protein lateral flow assay results supported those of the biochemical assays. Our results support those reported elsewhere that enhanced monooxygenase activity, at least in part, is responsible for neonicotinoid resistance in B. tabaci populations.