The provision of the sexually transmitted disease clinic service in the regional health authorities of England and Wales has been compared by relating the opening hours of clinics to the size of the population served. Relatively low levels of service were provided in the West Midlands and South-west Thames regions and high levels in the North-east and North-west Thames regions. When the service in the Greater London area health authorities was examined in relation to both resident and day-time populations, provision was relatively high in both instances, particularly in certain central London areas. Valid conclusions, however, about the equality of the service in different areas can only be drawn if the needs of the population for that service are known.