Prognostic value of DNA flow cytometry in paragangliomas of the carotid body. A carotid body tumor is a paraganglioma of the carotid bifurcation. Histologic appearance does not correlate with the malignant potential of the lesion, and thus a reliable prognostic marker for these tumors is lacking. To determine whether flow cytometric analysis of paraffin block specimens by DNA index and synthetic phase fraction (SPF) would be of prognostic value, a retrospective chart review of 14 patients with carotid body tumors was performed. Three of 14 tumors were aneuploid and were the only tumors with SPF greater than 15%. One of 3 patients (33%) with an aneuploid tumor (SPF = 22%) developed a local recurrence; no patient with a diploid tumor developed a recurrence. Two of 3 (67%) patients with aneuploid tumors (SPF = 18%) but only 1 of 11 (9%) with a diploid tumor were symptomatic preoperatively (P = 0.03). DNA index and SPF may help select a subgroup of patients with more aggressive tumors who are at increased risk for recurrence and therefore require closer follow-up. 