Background Nerve identification is recommended in inguinal hernia repair to reduce or avoid postoperative pain. The aim of this prospective observational study was to identify nerve prevalence and find a correlation between neuroanatomy and chronic neuropathic postoperative inguinal pain (CPIP) after 6 months. Material A total of 115 patients, who underwent inguinal hernia mesh repair (Lichtenstein tension-free mesh repair) between July 2018 and January 2019, were included in this prospective observational study. The mean age and BMI respectively resulted 64 years and 25.8 with minimal inverse distribution of BMI with respect to age. Most of the hernias were direct (59.1%) and of medium dimension (47.8%). Furthermore, these patients were undergoing Dermatome Mapping Test in preoperatively and postoperatively 6 months evaluation. Results Identification rates of the iliohypogastric (IH), ilioinguinal (II) and genitofemoral (GF) nerves were 72.2%, 82.6% and 48.7% respectively. In the analysis of nerve prevalence according to BMI, the IH was statistically significant higher in patients with BMI < 25 than BMI ≥ 25 P (< 0.05). After inguinal hernia mesh repair, 8 patients (6.9%) had chronic postoperative neuropathic inguinal pain after 6 months. The CPIP prevailed at II/GF dermatome. The relation between the identification/neurectomy of the II nerve and chronic postoperative inguinal pain after 6 months was not significant (P = 0.542). Conclusion The anatomy of inguinal nerve is very heterogeneous and for this reason an accurate knowledge of these variations is needed during the open mesh repair of inguinal hernias. The new results of our analysis is the statistically significant higher IH nerve prevalence in patients with BMI < 25; probably the identification of inguinal nerve is more complex in obese patients. In the chronic postoperative inguinal pain, the II nerve may have a predominant role in determining postoperative long-term symptoms. Dermatome Mapping Test in an easy and safe method for preoperative and postoperative 6 months evaluation of groin pain. The most important evidence of our analysis is that the prevalence of chronic pain is higher when the nerves were not identified.