Between 1910 and 1940 the Angel Island Immigration Station was the primary port of entry for Asians into the United States, the place of enforcement of the Chinese Exclusion Act and other anti-Asian immigration policies. Even in the absence of substantiating data, it is frequently asserted that almost all entering Chinese were detained at Angel Island and that they were detained for weeks, months, even years. This article presents the first empirical evidence on how long people arriving at San Francisco were detained at the Angel Island Immigration Station. The use of newly discovered data on passengers of the Pacific Mail Steamship Company (PMSS) for the period 1913-19 adds an empirical basis to our understanding of how immigration laws were administered in classifying and detaining aliens seeking to enter the United States, which arrivals were detained at Angel Island, and for how long. Results show that many Chinese were not detained at all; there was great variation in length of detention for Chinese who were detained; only some of this variation can be explained by the type of “exempt” status claimed for admission under the Chinese exclusion laws; Japanese arrivals had an even higher incidence of detention; and many detainees were either non-Asian, had come on ships from Central or South America, or were not “immigrants” at all.