The clinical characteristics of Caucasian adults with growth hormone (GH) deficiency (GHD) have been well defined. However, no large-scale clinical practice study has examined the clinical characteristics of Japanese adults with GHD. The aim of our study was to describe the clinical characteristics of Japanese adults with GHD by reviewing the records of participants who were GH-naive at the time of enrollment in the Hypopituitary Control and Complications Study (N = 349). The majority of participants (280 of 349; 80.2%) had adult-onset rather than childhood-onset GHD. Hypothalamo-pituitary tumors were the most common cause of GHD in Japanese adults (247 of 349; 70.8%); these tumors were primarily pituitary adenomas in participants with adult-onset GHD (156 of 243; 64.2%), and germ cell tumors (19 of 40; 47.5%) and craniopharyngiomas (18 of 40; 45.0%) in participants with childhood-onset GHD. Most participants (310 of 349; 88.8%) had multiple pituitary hormone deficiencies. Dyslipidemia (195 of 349; 55.9%), visual field loss (67 of 349; 19.2%), hypertension (59 of 349; 16.9%), and liver disease (54 of 349; 15.5%) were the most common pre-existing conditions in Japanese adults with GHD. Quality of life was decreased in seven of the eight short form-36 domains in participants with GHD compared with age- and sex-matched healthy Japanese individuals. Our findings confirm that the clinical characteristics of Japanese adults with GHD are similar to those of Caucasian adults with GHD. Confirmation of these clinical characteristics will enhance the ability of clinicians to identify and treat Japanese adults with GHD.