Clinical blood biochemistry and hematology are valuable tools to evaluate health and welfare in many animal species. In order to document the general biology of one of the most poorly known nonhuman primate species, and contribute to its conservation, the clinical blood biochemistry and hematology of the sun-tailed monkey (Cercopithecus solatusHarrisson) was investigated in its range of endemicity in Gabon. Data derived from 26 years of clinical monitoring of the only semicaptive colony of this species in the world, housed at CIRMF (Franceville, Gabon), were analyzed in order to establish reference values of age–sex classes. Consistent with previous reports in other primate species, age and sex significantly affected a number of biochemical and hematological parameters in C. solatus. Hematological analyses demonstrated significant differences in red blood cells, hemoglobin (HB), and hematocrit (HT), with males showing significantly greater values than females. In contrast, neutrophil counts were greater in females. An ontogenetic effect was detected for HB, HT, eosinophil, and monocyte counts, while lymphocytes significantly decreased with age. Biochemical analyses also showed significant differences, with females displaying greater cholesterol and alanine aminotransferase levels. Increase in levels of blood urea and aspartate aminotransferase coupled with decrease in albumin in old individuals suggested declining kidney, liver, and muscle functions with age. Interspecific comparisons were conducted and the effects of the unique semifree-ranging setting on the validity and value of the results presented are discussed. The reference values established will be useful in further ecological, parasitological, and virological studies of the sun-tailed monkey.