We used single photon emission computed tomography (SPECT) with [I-123]-labeled 2-((2-((dimethylamino)methyl)phenyl)thio)-5-iodophenylamine (ADAM) to investigate changes in serotonin transporter (SERT) availability in 10 morbidly obese young adults without an eating disorder (M/F = 5/5, body mass index (BMI): 40.3 ± 4.1 kg/m2, percentage of body fat (BF%): 46.0 ± 3.9%) and 10 age- and sex-matched non-obese controls (BMI: 20.3 ± 1.2 kg/m2, BF%: 20.6 ± 8.9%). Here, SLC6A4 is linked to eating disorder.