We report results of a search for the lepton-family number violating decay K+→π+μ+e− from data collected by experiment E865 in 1996 at the Alternating Gradient Synchroton of Brookhaven National Laboratory. We place an upper limit on the branching ratio at 3.9×10−11 (90% C.L.). Together with results based on data collected in 1995 and an earlier experiment, E777, this result establishes a combined 90% confidence level upper limit on the branching ratio at 2.8×10−11. We also report a new upper limit on the branching ratio for π0→μ+e− of3.8 × 10−10 (90% C.L.).