Color-blindness is the inability to perceive differences between some color that 
other people can distinguish. Using a literature search, the results indicate 
the prevalence of color vision deficiency in the medical profession and its on 
medical skills. Medical laboratory technicians and technologists employees 
should also screen for color blindness. This research aimed to study color 
blindness prevalence among Hospitals' Clinical Laboratories' Employees and 
Students in Tehran University of Medical Sciences (TUMS). A cross-sectional 
descriptive and analytical study was conducted among 633 TUMS Clinical 
Laboratory Sciences' Students and Hospitals' Clinical Laboratories' Employees to 
detect color-blindness problems by Ishihara Test. The tests were first screened 
with certain pictures, then compared to the Ishihara criteria to be possible 
color defective were tested further with other plates to determine color - 
blindness defects. The data was saved using with SPSS software and analyzed by 
statistical methods. This is the first study to determine the prevalence of 
color - blindness in Clinical Laboratory Sciences' Students and Employees. 2.4% 
of TUMS Medical Laboratory Sciences Students and Hospitals' Clinical 
Laboratories' Employees are color-blind. There is significant correlation 
between color-blindness and sex and age. But the results showed that there is 
not significant correlation between color-blindness defect and exposure to 
chemical agents, type of job, trauma and surgery history, history of familial 
defect and race. It would be a wide range of difficulties by color blinded 
students and employees in their practice of laboratory diagnosis and techniques 
with a potentially of errors. We suggest color blindness as a medical conditions 
should restrict employment choices for medical laboratory technicians and 
technologists job in Iran.