A maximum likelihood method of mixed distribution analysis (MDA) is presented as a method to estimate the prevalence of iron deficiency anemia (IDA) in Costa Rican infants aged 12-23 months old. MDA characterizes the parameters of the ad-mixed distributions of iron deficient anemics and non-iron-deficient anemics (NA) from the frequency distribution of hemoglobin concentration of the total sample population. Data collected by Lozoff et al. from 345 Costa Rican infants aged 12-23 months old were used to estimate the parameters of the IDA and NA hemoglobin distributions determined by MDA and the 3-criteria model of iron deficiency. The mean and standard deviation (SD) of the NA hemoglobin distribution determined by both methods was 12.1 +or- 1.0 g/dl. The IDA hemoglobin distribution determined by MDA had a mean and SD of 10.2 +or- 1.3 g/dl, while the IDA distribution by the 3-criteria method had a mean and SD of 10.4 +or- 1.3 g/dl. The prevalences of IDA as estimated by MDA and the 3-criteria method were 24% and 29%, respectively. The sensitivity and specificity of MDA were 95% and 97%, respectively. MDA performed similarly to the 3-criteria method at a simulated high prevalence of IDA and less similar at a low prevalence of IDA.