Individuals with intellectual disability (ID) have complex mental health needs and may seek specialized ID psychiatric services. This study reports on predictors of specialized inpatient admissions for 234 individuals with ID who received outpatient services at a psychiatric hospital. Overall, from 2007-2012, 55 of the 234 outpatients were triaged into the specialized inpatient unit. Aggression towards others and psychotropic polypharmacy significantly predicted these admissions. Unlike previous research, schizophrenia and level of ID did not predict admissions, suggesting that these factors may have a differential impact in specialized versus mainstream inpatient services. Findings are discussed in relation to how specialized inpatient units can be most responsive to these vulnerable patients and the factors that may impact clinical decision making.