The aim of our study was to evaluate the relationship between neutrophil to lymphocyte ratio (NLR) and adenoma size in parathyroidectomized patients who underwent a parathyroidectomy. The neutrophil to lymphocyte ratio has recently become popular as a biomarker for malignant diseases or for estimating tumor size preoperatively. This study aimed to estimate the relationship between adenoma size and NLR. Furthermore, we assessed whether a higher level of NLR is correlated with the presence of parathyroid carcinoma. A retrospective chart review was performed for patients with parathyroid adenoma who underwent parathyroidectomy between January 2012 and August 2014. Data related to age, sex, NLR, parathyroid hormone level (PTH), preoperative calcium, phosphorus, adenoma size, and pathology reports were collected. The neutrophil to lymphocyte ratio was significantly correlated with calcium levels, PTH levels, parathyroid adenoma size, and the presence of cancer. However, there was no correlation between NLR and age, sex, and phosphorus levels. This study is the first to document a positive correlation between NLR and parathyroid adenoma size, as well as the presence of cancer, in patients who underwent surgery as a result of primary hyperparathyroidism.