The use of unproctored Internet‐based testing (IBT) for personality assessment is increasingly popular, especially in personnel selection. Previous studies on its equivalence to traditional proctored paper‐and‐pencil testing (PPT) have used between‐subjects designs, which makes it difficult to separate intergroup effects from format effects, and have shown mixed results. The aim of the present study was to assess the quantitative, qualitative, and auxiliary equivalence of unproctored IBT and proctored PPT of personality, using a within‐sample design. Undergraduate students (n = 407) completed both an Internet and a paper‐and‐pencil version of a measure of the Big Five, with a 1 to 3 week interval. The proctored paper‐and‐pencil assessment was completed in class and the unproctored Internet assessment was completed at the time and place chosen by the participants. Results showed effect sizes for mean differences to vary from null to small. Skewness and kurtosis indices, reliability coefficients, intercorrelations magnitudes, as well as factor solutions, were highly similar across formats. Respondents did not prefer IBT over PPT on a series of statement about their perceptions and reactions to IBT. In conclusion, results suggest that IBT and PPT of the Big Five personality traits are equivalent, and that the data obtained are comparable across formats.