Background: Gastric cancer has a direct relation with chronic atrophic gastritis (AG) and intestinal metaplasia (IM), considered as preneoplastic lesions. Determination of serum pepsinogen I levels (PGI) and pepsinogen I/pepsinogen II ratio (PGI/PGII) can detect this conditions; achieving 70-90% of gastric cancer detection in early stages. Aim: To determine the cut-off values for serum PGI and PGI/PGII in chilean subjects, for the detection of gastric preneoplastic lesions, establishing their sensitivity, specificity, positive (PPV) and negative (ATV) predictive values. Patients and Methods: Prospective study of patients subjected to upper gastrointestinal endoscopy and determination of serum pepsinogen levels. The presence and severity of preneoplastic lesions were compared with serum levels of PGI and PGI/PGII. Results. A total of 56 men and 44 women were studied, with a mean age of 43 (14-77) years. There was a significant association (p <0.001) of PGI and PGI/PGII with AG and IM. We obtained a cut-off value of 2.3 for PGI/PGII (sensitivity = 70%, specificity =92%, FPV =60%, ATV =95%) and 36 ng/ml for PGI (sensitivity =62% specificity =64%, PPV =20%, APV =91%), for detection of moderate to severe AG. No patient with normal mucosa had a PGI <20 ng/ml. The combined criteria of PGI/II <= 2.3 and/or PGI <= 20 ng/ml, obtained a sensitivity of 85%, specificity of 92%, PPV of 65%, and NPV of 97%. Conclusions: We confirmed a strict relation of PGI and PGI/PGII with the presence of preneoplastic gastric lesions in Chilean patients.