Since the mid 1990s, early-onset bipolar spectrum disorders (BPSDs) have received increased attention in both the popular press and scholarly press. Rates of diagnosis of BPSD in children and adolescents have increased in inpatient, outpatient, and primary care settings. BPSDs remain difficult to diagnose, particularly in youth. The current diagnostic system makes few modifications to accommodate children and adolescents. Researchers in this area have developed specific BPSD definitions that affect the generalizability of their findings to all youth with BPSD. Despite knowledge gains from the research, BPSDs are still difficult to diagnose because clinicians must: (1) consider the impact of the child's developmental level on symptom presentation (e.g., normative behavior prevalence, environmental limitations on youth behavior, pubertal status, irritability, symptom duration); (2) weigh associated impairment and course of illness (e.g., neurocognitive functioning, failing to meet full DSM criteria, future impairment); and (3) make decisions about appropriate assessment (differentiating BPSD from medical illnesses, medications, drug use, or other psychiatric diagnoses that might better account for symptoms; comorbid disorders; informant characteristics and assessment measures to use). Research findings concerning these challenges and relevant recommendations are offered. Areas for further research to guide clinicians' assessment of children with early-onset BPSD are highlighted.