ABSTRACT Through a detailed assessment of nonspecific stress markers in 67 individuals (47 under 8 years old), this paper investigates the health conditions of preadults in Quebrada Chupacigarro Cemetery (QCC), North‐Central Coast of Peru, during the transition between the Middle and Late Formative periods (500–400 bc ), a critical time of sociopolitical change in the Central Andes. Our objectives are to determine (i) the nature of preadult morbidity and mortality, (ii) periods of greater vulnerability in the population, and (iii) the etiological factors associated with health–disease processes in this context of population pressure. The results show a high prevalence of anemia‐related stress markers in preadults with a strong selective mortality in < 3.5‐year‐old individuals, and recurrent periods of adult morbidity. These findings indicate exposure to disease because of overcrowding, lack of sanitation and malnourishment, and support the idea of precarious living conditions in the Supe Valley around 500–400 bc .