Introduction: Occupational heat exposure is a major occupational health issue and a great number of indoor workers may be at risk of heat stress and its consequences, particularly those working near a radiant heat source as in kitchens. Aim of Work: To assess heat stress in hospital kitchen environment through environmental heat measurements using the wet-bulb globe temperature index , to evaluate the prevalence of heat related illness and to detect the impact of chronic indoor occupational heat exposure on the kidney health and functions through measurement of urinary interleukin-18 and neutrophil gelatinase-associated Lipocalin. Materials and Methods: A cross sectional comparative study was conducted upon 87 workers in a large scale hospital kitchen at Cairo, Egypt. The workers were classified into two groups: the directly heat exposed group (40 cookers) who were directly in contact with thermal radiation. The second group was the indirect heat exposed group (47 workers) who were involved in activities away from heat contact. Both groups were subjected to a detailed questionnaire including history of self-reported heat related heat illnesses, clinical examination, measurement of urinary levels of interleukin-18 and neutrophil gelatinase-associated Lipocalin. Environmental heat measurements at different workplaces were assessed. Results: In the cooking areas, the mean value of wet-bulb globe temperature was (32.4±1.4) that exceeded the threshold limit value (TLV) recommended by American Conference of Government Industrial Hygienists (28°C). The median and interquartile range of urinary biomarkers were significantly higher among the directly heat exposed group (32.4, 22.7-51.9 and 102.6, 77.9-161.5) for interleukin-18 (IL-18) and neutrophil gelatinase-associated Lipocalin (NGAL) respectively. There was a statistically significant fewer water cups drunken by the direct heat exposed workers (p value ˂0.001). The direct heat exposed group reported highly significant occupational heat related symptoms as heat cramps, excessive sweating, headache, dizziness, fatigue/ tiredness and excessive thirst (p < 0.001). Conclusion: The current study revealed that kitchen workers particularly cookers were chronically exposed to excessive indoor heat stress exceeding the permissible limit producing heat related illness and subclinical kidney affection.