To assist long-term protection of roost sites, roosting patterns of California Brown Pelicans (Pelecanus occidentalis californicus) at San Nicolas Island (SNI), California, were assessed for the 1972–2006 period. SNI was used for roosting year-round, with most birds likely from nearest primary breeding colonies (Santa Barbara and Anacapa islands) within the Southern California Bight subpopulation. Among non-El Niño years, monthly diurnal counts varied, but ranged from less than 100 birds during the breeding season to approximately 1,000 during fall. Influxes from the large Gulf of California subpopulation also occurred on occasion, best demonstrated by prolonged increased numbers during strong El Niño conditions in 1972–1973, possibly reflecting delayed or skipped breeding and increased prey availability near the outer California Channel Islands. The peak estimate of 13,500 night-roosting pelicans was on 16 November 1972 during these El Niño conditions. Most pelicans roosted diurnally on the north shore, reflecting close proximity to main foraging areas. Diurnal roost patterns did not appear affected by introduced feral cats (Felis catus) and Island Foxes (Urocyon littoralis dickeyi). The single, major night roost shifted 4 km from Cormorant Rock Area (used 1972–1992) to Vizcaino Point by 2006, following reduction of human disturbance in 1992–1996. Vizcaino Point and Cormorant Rock Area should be designated as “key, long-term roosts” that merit additional protection. Received 25 July 2011, accepted 14 March 2012.