Clinical and histologic features of 38 cases of neuroblastoma were compared with data obtained by flow cytometric DNA analysis. Favorable clinical outcome was associated with an aneuploid stem line (P less than 0.01) and a low percentage of tumor cells in the S, G2, and M phases of the cell cycle (P less than 0.005). These favorable cytometric features were also associated with a favorable clinical stage (1, 2, 4s), and histologic evidence of Schwann's cell and ganglion cell differentiation. Consideration of cytometric data improved the sensitivity, specificity, and predictive efficiency of a current system for histologic grading of neuroblastoma.