Fine-needle aspiration biopsy (FNAB) is the most accurate diagnostic method to assess the malignancy risk of thyroid nodules. However, non-diagnostic results may delay diagnosis, cause unnecessary interventions, and distress patients. We aimed to determine whether a correlation exists between patients' situational anxiety, pain perception and non-diagnostic cytology results. The prospective study included patients who underwent thyroid FNAB at the Endocrinology Clinic of Sultan Abdulhamid Training and Research Hospital between 11/2022 and 02/2023. The State-Trait Anxiety Inventory (STAI) questionnaire and visual analogue scale (VAS) assessed situational anxiety and pain in patients undergoing biopsy procedures. We evaluated whether the STAI-S and VAS score is related to non-diagnostic results. Of the 119 patients included in the study, 98 were female, and 21 were male. 25 (21%) nodules were non-diagnostic. The patients' mean STAI-S score before the biopsy was 47.31±12.37, and the mean VAS score after the thyroid biopsy was 2.57±1.51. A statistically significant relation was found between the patient's STAI-S score and VAS score and the cytology result of non-diagnostic (p= 0.001 and p=0.008). In univariate logistic regression, high pre-procedural anxiety (OR:3.09, 95% CI:1.07-8.94, P =0.037) and VAS score (OR:1.57, 95% CI: 1.17-2.10, P =0.002) were associated with non-diagnostic cytology. In multivariate logistic regression analysis, VAS score (OR: 1.59, 95% CI: 1.07-2.34, p=0.019) was still an independent factor related to specimen adequacy. Anxiety level and pain perception during FNAB may be considered risk factors for non-diagnostic cytology. Thus, reducing anxiety and pain may decrease the incidence of non-diagnostic outcomes.