Objectives: To develop methods for early detection of natural killer/T-cell lymphoma, nasal type (nasal NKTL) and to evaluate the use of apparent diffusion coefficient (ADC) measurements from diffusion-weighted imaging (DWI) for selecting biopsy sites to enhance the positive biopsy rate. Methods: The clinical data of 32 cases of nasal NKTL were retrospectively collected and analyzed. Cases were graded from 1 to 5 based on endoscopic and imaging findings. Biopsy methods included the superficial forceps method and deep incisional method. Data recorded included biopsy method, time to confirmed diagnosis, number of biopsies required, and ADC values of biopsy sites. Results: Both endoscopic and MRI lesion severity did not affect biopsy outcomes (p = 0.8248, 0.7571). The deep incisional biopsy method had a significantly higher probability of yielding positive pathological results compared to the superficial clamping method [OR (95% CI) = 23.2143 (6.0448, 89.1513) (chi(2) = 26.1089, p < 0.0001)]. The ADC value at the site with a positive biopsy result is significantly lower than at the site with a negative result (p = 0.0003). The diagnostic threshold for ADC value to predict a positive biopsy result was 0.603 x 10(-3) mm(2)/s, with a Youden index of 0.43. Conclusions: Nasal NKTL has distinct characteristics distinguishing it from sinusitis and other tumors. Deep incision biopsy under general anesthesia is superior to the superficial method. The location of the positive sampling site can be guided by measuring the ADC value, and the optimal diagnostic threshold of this proposed method is 0.603 x 10(-3) mm(2)/s. Level of Evidence: 4 Laryngoscope, 2024