OBJECTIVE: Human growth hormone (GH) is well established as a treatment for growth hormone deficiency. Recently, a new liquid GH formulation (Norditropin SimpleXx®) has become available that does not require reconstitution before subcutaneous self-administration with a new delivery system (NordiPen™) and an optional auto-injector (NordiPenmate™). In this study the acceptability and tolerability of and compliance with the liquid formulation were investigated DESIGN AND PATIENTS: An open 6-week multicentre trial in 53 patients, including adults and children, was performed in The Netherlands. Acceptability and tolerability of the liquid GH formulation were assessed by questionnaires and compliance by both questionnaires and re-collection of GH cartridges MAIN OUTCOME MEASURES AND RESULTS: The mean daily dosage of GH was 0.24 mg/m2 (0.03 to 0.82 mg/m2) in adults and 1.13 mg/m2 (0.65 to 1.77 mg/m2) in children. Most patients (91% of adults and 89% of children) preferred to continue on the new GH formulation rather than the previously used formulation. This was mainly due to the easier and less time-consuming procedure and the good tolerance of the drug. Self-reported compliance also improved, but this could not be proven due to poor return of study cartridges CONCLUSIONS: The use of the liquid GH formulation Norditropin SimpleXx® with the NordiPen™ device and optional use of the NordiPenmate™ device was well accepted by both adults and children. This was mainly due to the avoidance of reconstitution and the ease of handling of the injection device.