Despite sleep problems being part of the diagnostic criteria for mood disorders, research on sleep difficulties related to early-onset bipolar spectrum disorders (EBSDs) is sparse. The authors examined the parent and child agreement, frequency, and severity of EBSD-related manic, depressive, and comorbid sleep problems. A sample of one hundred thirty-three 8- to 11-year-olds with EBSDs was assessed with parental and self-report measures of EBSD-related sleep problems. Dimensional and categorical measures indicated low agreement and high discrepancy between parent and child reports of EBSD sleep problems. Subsequent combination of parent-child data revealed the majority (96.2%) of children had moderate-to-severe sleep problems related to manic, depressive, or comorbid symptoms, either currently or during their worst mood period. More depression-related sleep problems than mania-related sleep problems were reported, especially initial insomnia. Over half the sample had sleep problems associated with current comorbidity, particularly separation anxiety disorder. These findings, their implications, and study limitations are discussed.