Acetone is qualitatively known as a biomarker of diabetes; however, the quantitative information on acetone concentration in diabetic breath is incomplete, and the knowledge of correlations of breath acetone with diabetic diagnostic parameters, namely, blood glucose (BG) and glycohemoglobin A1C (A1C), are unknown. We utilized a pilot-scale breath acetone analyzer based on the cavity ringdown spectroscopy (CRDS) technique to conduct breath tests with 34 Type 1 diabetic (T1D), ten Type 2 diabetic (T2D) patients, and 15 apparently healthy individuals. Relations between breath acetone and BG, A1C, and several other bio indices, such as the type of diabetes, onset-time, gender, age, and weight were investigated. Our observations show that a linear correlation between the mean group acetone and the mean group BG level does exist (R = 0.98, P < 0.02) when all the T1D subjects tested are grouped by different BG levels, 40-100, 101-150, 151-200, and 201-419 mg/dL. Similarly, among the T1D subjects studied, when their A1C's are grouped by < 7, 7-9.9, and 10-13, a linear correlation between the mean group A1C and the mean group acetone concentration is observed (R = 0.98, P < 0.02). No strong correlations are observed when the BG and A1C numbers are not grouped. The mean breath acetone concentration in the T1D subjects studied in this work is determined to be 2.19 ppmv (parts per million by volume), which is higher than the mean breath acetone concentration, 0.48 ppmv, in the 15 healthy people tested.