Objective[|]Obstructive sleep apnea syndrome (OSAS) is described as repetitive apnea episodes that lead to inflammation, ischemia/hypoxia, and may also have effects on mineral and metabolic markers. We aimed to examine the relationships between calcium (Ca), magnesium (Mg), the Ca/Mg ratio, insulin sensitivity–resistance markers (glucose, insulin, homeostatic model assessment indicator of insulin resistance (HOMA-IR)), cardiovascular markers (lipids, lipoproteins), and their relationships with each other, and to find out the possible influence of Ca/Mg ratio on metabolic markers in OSAS.[¤]Materials and Methods[|]Male patients’ metabolic markers and mineral levels were compared with those of control subjects.[¤]Results[|]In the OSAS group, fasting glucose and insulin levels were statistically significantly higher (p=0.004 and 0.003, respectively), and fasting glucose levels were correlated with Ca, Mg, and Ca/Mg ratios (0.012, 0.001, and 0.000, respectively). Calcium levels were correlated with HOMA-IR (p= 0.015). Severe OSAS patients had a statistically significantly higher Ca/Mg ratios (p=0.017) and HOMA-IR levels (p=0.003) than mild/moderate group, but the correlation between the Ca/Mg ratio and HOMA-IR was not statistically significant.[¤]Conclusion[|]Mg and Ca levels appear to be related to insulin resistance markers in patients. Severe OSAS patients had statistically higher Ca/Mg ratios than mild/moderate groups, so they might represent a risk group with respect to diabetes.[¤]