This is an overuse injury to the neck of the femur bone, where the rate of damage to the bone exceeds the body's ability to repair it. It is commonly an overuse injury in female runners. Paula Radcliffe suffered this injury.
It presents as groin pain, initially only with activity, but gradually becoming present at rest. It gets worse over a period of weeks and can cause pain at night, then constant pain. Pain is worse with weight bearing exercise and there is often an area of quite specific tenderness.
If you think you have this condition it is well worth getting it checked as soon as possible by Mr Willis-Owen. You should avoid any aggravating activities with may make things worse. It will not get better on its own, unless you significantly alter your activities. If you try to ignore it, it may progress to a fully displaced fracture which can be devastating.
Treatment involves first confirming the diagnosis which is not particularly easy in the early stages. X-rays may miss the injury and MRI scanning or bone scanning is more helpful. A period of relative rest will be required and this may involve the use of crutches. This will be followed by rehabilitation to work on stretching and strengthening. It is important to identify why you developed a stress fracture and to identify any underlying problems, which may make you at risk of recurrence.
Mr Willis-Owen has had success using an Exogen bone stimulator to accelerate the healing of stress fractures.