Children and young people living with severe obesity experience a range of complications of excess weight (CEW); however the prevalence of complications is not well defined. We have evaluated baseline characteristics and CEW of patients from two UK tier 3 paediatric weight management services. All new patients aged 2-17 years seen from March 2022 to February 2023 were included. Baseline demographic data was collected, and patients screened for CEW. PedsQL-4.0 questionnaires were used to assess health-related quality of life (HRQL). 185 patients were included, median age 14.3 years (range 3.3-18.0), 50.8% were girls. Of the patients, 73.8% were white British, with a significant excess of patients living in the most deprived decile (41.4%). Median body mass index SD score was +3.55 (IQR 3.11-3.90) and median body fat was 49.3% (IQR 42.3%-55.1%). Autistic spectrum disorder, attention deficit hyperactivity disorder and learning difficulties were vastly over-represented.Dyslipidaemia was the most common (51.6%) complication, followed by hypertension (28.9%), metabolic dysfunction-associated steatotic liver disease (17.8%), obstructive sleep apnoea (9.0%) and idiopathic intracranial hypertension (4.3%). Mean glycated haemoglobin was 35.0 mmol/mol (IQR 33-38). 8.1% had type 2 diabetes mellitus. Many of these complications were detected through screening in CEW clinics.Both child-reported (mean 51.9/100) and parented-reported (47.8/100) HRQL scores were low. Mental health problems were common: 26.2% with anxiety and 7.7% with depression. This study demonstrates the significant and profound mental and organ-specific pathology resulting from severe obesity in childhood, highlighting the clinical necessity for CEW clinics. A rigorous approach to identify complications at an early stage is essential to improve long-term health outcomes.