I have short sleeve jersey's in medium but decided to go with a large size on the long sleeve. I LOVE the fit. For reference I'm 5'5", 125lbs with broad shoulders. I am confident the medium long sleeve would have worked as well with a fitted look, but then I could not layer underneath. With the large I have good movement in the shoulders and the sleeves are loose. If you want this to fit tighter then stay with your regular jersey size. The long sleeve has a good weight but not too heavy. Will be perfect for fall and spring rides in southern USA and I'll add a base layer in the winter. The colors are vibrant and great for visibility.