Adolescents and young adults with Marfan syndrome (MFS) use information from self-surveillance to manage their disorder. Thirty-seven male and female adolescents with MFS aged 14 to 21 years were interviewed. They identified 58 distinct self-surveillance behaviors that fell into four categories and multiple subcategories (SCs): tracking phenotype (SCs: physical appearance, physical fitness, medical problems, and other observations); tracking medical care (SCs: medical evaluations and treatments, and pharmacotherapy); tracking behavior (SCs: personal choices and social relations); and tracking emotions (SCs: positive emotional impact and negative emotional impact). The frequency and range of self-monitoring increased with the age of the child. On average, a child of 14 self-monitored from 1 to 3 times per day, whereas a person aged 21 might self-monitor many more times per day. The patient-parent-physician relationship is the context for teaching adolescents and young adults self-surveillance skills. Self-surveillance by patients is first-line symptom assessment and an adjunct to medical monitoring. (Contains 2 tables and 1 figure.)