We aimed to construct and assess a new self rating scale to detect the side effects of second generation antipsychotics. This scale was designed to allow a timely, sensitive and reliable method of gathering information on the number and severity of side effects an individual suffers from. The Glasgow Antipscyhotic Side-effect Scale (GASS) was developed after literature review, discussion with members of the mental health team and with service user feedback. Fifty indivudals taking second generation antipsychotics completed the GASS along with the Liverpool Univeristy Neuroleptic Side Effect Rating Scale, and one week later completed the GASS for a second time. Fifty comparison subjects also completed the GASS. The GASS was shown to have good discrimatory power and construct validity, along with good re-test reliablity, and is put forward as a short, helpful and valid clinical tool.