The prevalence of childhood obesity has more than tripled over the past five decades. Obesity results in low lung volumes, likely through increased loading of the chest wall and abdomen. The prevalence of asthma in children has paralleled the rise in obesity; obesity may increase the severity of asthma, but a direct link has been difficult to establish. Obesity is a risk factor for obstructive sleep apnea (OSA) in children as well as adults. Obese children may be at increased risk for persistent OSA following adenotonsillectomy treatment for OSA. Severe obesity and OSA may lead to the obesity-hypoventilation syndrome, with hypoxia, hypercapnia, and reduced ventilatory drive. Obesity can increase a child's risk for complications of anesthesia and recovery from surgery.