Five common medical conditions among opioid substitution therapy (OST) clients were assessed during a health promotion event held at a tertiary hospital-based OST clinic in Sydney, Australia. Data were collected anthropometrically (body mass index and waist circumference), using spirometry, electrocardiogram, Pap test histories, Fibroscan and medical record review. Assessments were undertaken by specialised hospital staff. Abnormal results were found for 17% of those who underwent an electrocardiogram, 60% were anti-hepatitis C virus positive (40% were viraemic), fibrosis was detected in one-third (7% severe fibrosis and 18% cirrhosis), chronic obstructive pulmonary disease was detected among 30% of participants with 7% at Global Initiative for Chronic Obstructive Lung Disease stage II and 2% at stage III. Forty-seven percent of the female respondents reported that they had not had a Pap test in the previous 2 years. Findings indicate that OST clients suffer several health problems that OST clinics are well placed to identify and provide support for referrals.