Background: Both performer- and device-dependent variabilities have been reported in sizes of wheal responses to skin prick tests. Objective: We aimed to evaluate whether or not variabilities in sizes of wheal responses influence the final interpretation of skin prick tests; in other words, the decision on whether or not there is an allergy to a given antigen. Methods: Skin prick tests with positive and negative controls and extracts of Dermatophagoides farinae and Dermatophagoides pteronyssinus were done for 69 patients by two different persons, using two different puncturing devices- disposable 22-gauge hypodermic needles and metal lancets. Results: Among four different skin prick tests, the average coefficients of variation in sizes of wheal responses were near to or higher than 20% for all of them. On the other hand, in the final interpretation of results, kappa values indicated substantial or almost perfect agreements between these tests. However, the frequency of establishing allergy to the house dust mites widely ranged in these tests (20.8–35.8% for D. farinae and 20.8–28.3% for D. pteronyssinus). Limitations: The conduction of the study in a single center and the comparisons of results of only two performers. Conclusion: We feel that variabilities in sizes of wheal responses of skin prick test can influence its categorical results.