We conducted a prospective, observational study of patients presenting to an emergency department with suspected use of a street drug known as "illy" to identify the active ingredient in "illy" and describe the clinical presentation and outcomes associated with its use. Vital signs, mental status, restraint use, and urine toxicology (UT) results were recorded. Patients were interviewed about drug use patterns and co-ingestants. Fifty-nine patients (89.9% males) with a mean age of 22 years (SD +/- 4.37) were enrolled over a 34-month period. UT was obtained in 61% of patients; of these 91.7% tested positive for phencyclidine (PCP). Seventy-eight percent of patients were discharged, (15.3%) required psychiatric evaluation; 3 were admitted, one died in the ED. Patients reported concurrent drug use (54%) and at-risk drinking (50%). PCP is likely the active component of "illy". Most patients require observation and supportive care only, however major complications including death may occur.