OBJECTIVE The study objective was to fill research gaps about inpatient psychiatric service utilization among Asian Americans and Pacific Islanders (AA/PIs). METHODS Rates of psychiatric hospitalization, illness severity, and length of stay were compared among AA/PI adults overall and across diagnoses (schizophrenia, depression, bipolar, anxiety, and other psychiatric disorders identified by All Patient Refined Diagnosis Related Groups) by using discharge data from all hospitalizations in Hawaii from December 2006 to 2010. Multivariable models adjusted for gender, age, payer, and residence. RESULTS In multivariable analyses of total psychiatric hospitalizations, Chinese (rate ratio [RR]=.22), Japanese (RR=.23), Filipinos (RR=.30), and Native Hawaiians (RR=.37) had significantly lower rates than whites. Native Hawaiians had significantly higher hospitalization rates compared with other AA/PI groups. Length of stay was significantly longer for Chinese (length of stay ratio [LOSR]=1.53), Filipinos (LOSR=1.20), and Japanese (LOSR=1.19) compared with whites, whereas severity of illness was significantly higher for Japanese (odds ratio [OR]=1.36) and Filipinos (OR=1.30). Within specific diagnoses, Native Hawaiians had higher hospitalization rates than other AA/PI groups for depression, bipolar disorder, and anxiety disorder. Chinese, Japanese, and Filipinos had significantly higher illness severity or longer stays than whites for at least one diagnostic category. CONCLUSIONS AA/PI subgroups had lower psychiatric hospitalization rates than whites, but rates varied across AA/PI subgroups. Native Hawaiians had higher hospitalization rates for many diagnoses. Chinese, Japanese, and Filipinos had greater illness severity or longer stays than whites overall and for some diagnoses, whereas Native Hawaiians did not. Disaggregating AA/PI groups provides important insight into mental health services utilization and need.