Aim: To determine the variation of hemoglobin (Hb) in two groups of miners working at different altitudes. Methodology: A longitudinal study conducted in a private company. Hb was obtained from entrance exams and annual checks of workers at two locations: at sea level and at Peruvian highlands (4,100 m), taken by trained staff and equipment calibrated to environmental conditions. We analyzed variations in the course of the years with the PA-GEE statistical test; p values were obtained. Results: Of the 376 workers, 89[%] (322) were men, the median age was 32 years (range 20-57) and 84[%] (304) were at high altitude. In multivariate analysis, male sex (p < 0.001), body mass index (BMI; p = 0.021) and working at high altitude (p < 0.001) were associated with the greatest variation of Hb in time, adjusted for age, length, and type of work. Discussion: These findings should be considered for health surveillance of workers exposed to similar conditions to prevent chronic mountain sickness. Conclusion: The change in Hb of miners was associated with male sex, BMI, and work at high altitude.