Both insulin resistance (IR) and vitamin D deficiency (VDD) are found to be associated with many cancer types. In this study, we evaluated the presence of IR and VDD in thyroid cancer patients based on controls. Total 344 papillary thyroid cancer and 116 controls were part of the study. Glucose, insulin, homeostasis model analysis-insulin resistance (HOMA-IR) (control group 2.12 ± 0.9 and patient group 3.6 ± 1.1; p < 0.0001), LDL were significantly high; HOMA-S and vitamin D3 levels (control group 19.11 ± 8 and patient group 17 ± 16; p = 0.004) were significantly low in the patient group. Vitamin D deficiency (64/108 in controls vs 166/235; p = 0.026) and insulin resistance (24/108; 115/235; p < 0.0001) were more frequent in papillary thyroid cancer patients. After regression analysis, tumor diameter showed significant association with log-HOMA-IR (B = 0.315; p = 0.017) and log-vitamin D3 (B = 0.207; p = 0.04). Vitamin D deficiency and insulin resistance frequencies show no difference between micro- and macropapillary thyroid cancers. Receiver operating characteristic curve shows the best cutoff point for tumor diameter showing that the presence of lymph node metastasis was 0.65 cm with 81.2 % sensitivity and 52 % specificity. Best cutoff point for the capsular invasion tumor diameter was 0.75 cm with 83.3 % sensitivity and 60.4 % specificity. No difference between follicular and classical type papillary thyroid carcinomas has been yet discovered. As a result, thyroid cancer patients are more insulin resistant and vitamin D3 deficient. Vitamin D3 levels and HOMA-IR index may affect tumor diameter. Tumor size that is lower than 1 cm (0.65-0.75 cm) may be related with capsular invasion and lymph node involvement.