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.