N-nitrosamines, widespread contaminants, can be formed from precursors in food including nitrites and amines. The effects of six cooking methods (roasting, stir frying/griddling, frying, blanching, boiling, and others) were investigated in terms of the concentrations of seven N-nitrosamines including N-nitrosodimethylamine, N-nitrosomethylethylamine, N-nitrosodiethylamine, N-nitrosodibutylamine, N-nitrosopiperidine, N-nitrosopyrrolidine, and N-nitrosomorpholine in Total Diet Study samples. In conclusion, N-nitrosodimethylamine, N-nitrosodiethylamine, and N-nitrosopyrrolidine increased during boiling (5.26, 1.42, and 1.31 μg/kg each, p < .05), N-nitrosodiethylamine contents increased in blanching, roasting induced N-nitrosodimethylamine increases, and microwave heating increased N-nitrosodiethylamine concentration (0.25, 1.73, and 0.15 μg/kg each, p < .05). Overall, N-nitrosodimethylamine was the most frequently detected N-nitrosamine (51.0%), boiling produced the most N-nitrosamine, and N-nitrosamines were found most frequently in fish samples. Based on the results, we recommend avoiding boiling or discarding boiled water to reduce risk from the food-borne N-nitrosamines. This research could improve our understanding of N-nitrosamine changes by cooking in wide ranges of food products. Practical applications N-nitrosamines can increase during boiling, blanching, roasting, and microwave heating. Boiling fish and cooking with seasoning might cause significant increases in N-nitrosamines. Because N-nitrosamines are not good for humans, cooking methods and food ingredients should be considered carefully.