I would recommend taking it early during your second year of residency. Internship experience (admissions, assessments, plans, etc) really helps, especially with those case studies. Plus there is a Blueprints-CCS that I HIGHLY recommend you read 3-4 times before Step 3. If you want I can recommend some good study aids. I scored a 99 on it. 😀 By the time you start third year you need to be sleeping with MKSAP, so you won't want to study for Step 3 that late.