Objective: To examine the relation of caregiver ratings of psychiatric symptom-induced impairment with number and severity of symptoms and informant agreement in consecutive child psychiatry outpatient referrals. Methods: Parents and teachers completed a broadband "DSM-IV"-referenced rating scale with disorder-specific impairment for 636 youth (6-18 years). Illness parameters included impairment, number and severity of symptoms, and their combination (symptom + impairment) as well as categorical (cut-off) and dimensional scoring. Results: Agreement between impairment and other illness parameters showed considerable variation as a function of type of parameter, disorder, and informant, but to lesser extent age and gender. Many youth who met impairment cut-off for specific disorders did not meet symptom cut-off. Conversely, most youth who met symptom cut-off were impaired. Symptom cut-off evidenced greater convergence with impairment cut-off than combined symptom + impairment cut-offs. Severity of impairment was moderately to highly correlated with number and severity of symptoms. Parents' and teachers' ratings indicated little disorder-specific agreement about youth who met impairment cut-off, symptom cut-off, or combined symptom + impairment cut-off. Therefore, sole reliance on one informant greatly underestimates the pervasiveness of impairment. Conclusion: Findings are consistent with the notion that each illness parameter represents a unique conceptual construct, which has important clinical and research implications.