Growing pains are typically non-articular, intermittent bilateral aches or pains in the legs that occur in the evening or at night in children aged 3-12 years. They are not associated with limping or limited mobility and do not involve the joints (all of which are recognised signs of pathology); no signs of local trauma or infection are seen."

Source : BMJ. 2006 Sep 2; 333(7566): 456–457.

The condition is extremely widespread - current estimates are that it affects between 10 and 40% of all children at some stage.

The cause is unknown.

Despite its name, coined almost 200 years ago, current research is suggesting that the pains are not associated in any way with bone growth - leading some researchers to suggest a re-naming of the condition.

Other possible causes are currently under investigation ::

The idea that growing pains are caused by rheumatic fever was disproved in the 1930s. Subsequent causal theories include faulty posture and an association with restless leg syndrome, vascular perfusion disorder, fatigue, or emotional disturbance.

[Source as above]