No special requirements to my knowledge -- though if you're really concerned, I'd suggest contacting a Lao Embassy just to be sure.
Closest border crossing to Chiang Mai is the Chiang Khong/Huay Xai crossing -- there are direct buses from Chiang Mai or you can overnight at Chiang Rai.
More information on border crossings here.
#2 somtam2000 has been a member since 21/1/2004. Location: Indonesia. Posts: 7,798
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