This thesis examines two emerging issues in sexual health; Mycoplasma genitalium, a relatively recently discovered STI, and 'stealthing', a recently discussed sexual practice. Overall, the thesis has contributed to the international literature on the prevalence of Mycoplasma genitalium, and its contribution to clinical presentations in men and women, including PID and co-infection, and provides the first estimates of 'stealthing' in a large population of sexual health attendees.