Dr. Klein graduated Magna Cum Laude from Dartmouth College and finished medical school at Cornell in 1973. His medical internship was at the University of New Mexico before serving in the US Public Health service for two years. He completed his residency in Internal Medicine at University of California, San Francisco. He is board certified in both Internal Medicine and Infectious Diseases and is a Fellow of the Infectious Disease Society of America.
In 1983, he was named Chief of Infectious Disease for Kaiser Permanente southern Alameda County. He was the recipient of numerous awards for clinical expertise and research achievements. He coauthored dozens of publications and peer reviewed poster presentations on HIV topics. He served as chair of the Northern California Kaiser HIV committee and was the first chair of the Kaiser National Consortium on HIV research.