I have a sixteen month old son for the last 8 weeks I have noticed a medium size hard lump on his head. It is situated more or less behind his left ear but on the scull the opposite side is clear and smooth no lumps at all anywhere else on his head. It does not bother him nor is there any discolouring of the skin. Not too sure whether I should be concerned and take him to the doctor.

If it wasn't there before and it's there now or if it's not on both sides of his head, yes, as his mother I think a Doctor has to look at it. Could be anything and why take a chance - ?

While it could be nothing more than a swollen lymph node, there are reasons for swollen lymph nodes. Some very simple and some very complex.

Please do not leave the health of your infant in the hands of complete strangers over the internet. Get that baby to a doctor.