What a coincidence. I was just at the pharmacy refilling my son's solucortef prescrip today and had this exact conversation with the pharmacist. From previous prescrips, I have everything from a 22g needle to a 27g?. Here is what the pharmacist told me: She said to consider (1) the gauge of the needle. It has to be strong enough to break through the cork? stuff to get into the solucortef, small enough to hurt the least possible, and big enough for the solucortef to flow freely (2) the length of the needle. It has to be longer for intramuscular injections (3) The size of the syringe. It is a balance between big enough for the amount and small enough to be well marked. What I ended up with is a 3ml IM 23 gauge with 1 1/2 inch needle. She also gave me 25 gauge needles in case we wanted to withdraw the solution with the 23 gauge and then switch to the 25 for injection. My son is 2 years old. He has an appt with his endo next week and I will check for her opinion. I am very interested to hear what everyone else uses. Thanks for the good post Michele.