I bought size 18 month for my 16-month old son to wear, and it fit and looked great.  He seemed to enjoy wearing it.  We just put a long-sleeved onesie and pants underneath.  The suit was slightly large meaning sometimes his hands disappeared into the sleeves and there was some gathering at the bottom.  He was maybe 32 inches tall at the time and sort of slender.  It is first-rate quality, including the hat.  The white suit was cheaper than the orange, and my husband informed me that the white was 'old school' and he preferred it.