Sleep problems are common in adolescence and recognized as an international public health concern given their links to a range of adverse outcomes. Adolescents with attention-deficit/hyperactivity disorder (ADHD) experience more sleep problems than their peers, including delayed sleep onset, shorter sleep duration, poorer sleep quality, more sleep variability, and greater daytime sleepiness. Further, research conducted by the investigator's team has shown that sleep problems are strongly associated with - and causal contributors to - functional impairment in adolescents with ADHD, including increased mood, behavior, and academic problems. However, sleep problems are not currently addressed in any evidence-based treatment for adolescents with ADHD, and no study has evaluated an intervention targeting sleep problems in adolescents with ADHD. This is a notable gap in the field since consensus statements on sleep suggest that treating sleep problems may improve ADHD and associated impairments. Evidence-based cognitive-behavioral sleep interventions, including the Transdiagnostic Sleep and Circadian Intervention for Youth (TranS-C) intervention, are effective for improving sleep and associated impairments (e.g., attention, mood) in adolescents with sleep problems. However, these interventions have never been tested in adolescents with ADHD specifically. This will be the first to evaluate a cognitive-behavioral sleep intervention (TranS-C) in adolescents with ADHD who experience co-occurring sleep problems. This study will recruit 15 adolescents with ADHD and sleep problems to enroll in and complete an open trial of the TranS-C intervention to evaluate its feasibility, acceptability, and preliminary efficacy. Findings will provide key pilot data regarding treatment of sleep problems in adolescents with ADHD.

Inclusion Criteria:

1. Between 13 and 17 years of age at the first TranS-C session.
2. Estimated IQ ≥ 80 as assessed by the Kaufman Brief Intelligence Test, Second Edition (KBIT-2).
3. Meet full DSM-5 criteria for ADHD (per protocol).
4. Meet criteria for sleep problems (per protocol).
5. Sufficient English language ability necessary to complete study measures and intervention per parent and/or research staff judgment.
6. If applicable: If the adolescent is taking a medication for ADHD or another psychiatric disorder (e.g., anxiety, depression), the adolescent must be on a stable medication dose/schedule for at least one month, and families will also be asked to not change/add medications the adolescent takes during the intervention period.

Exclusion Criteria:

1. Children who have participated in a behavioral or cognitive-behavioral sleep treatment in the past year will be ineligible.
2. Children with a parent-report diagnosis of autism spectrum disorder, bipolar disorder, obsessive-compulsive disorder, or psychosis will be excluded.
3. Children taking a prescribed medication for sleep problems per parent report (not including melatonin).
4. Significant visual, hearing, or speech impairment not helped with corrective or assistive devices (e.g., glasses, hearing aids) per parent report or study staff judgment.