Scuba Nation Cambodia - PADI Diving and Instruction in the Gulf of Thailand (Sihanoukville and Phnom Penh)
Routes to get to Sihanouville from Laos, Vietnam, Thailand and from within Cambodia

You have several options to travel from Malaysia to Cambodia and it depends on your time and budget.

The fastest option:
Fly to Phnom Penh from Kuala Lumpur and there are several flight companies who offer daily flights. The one we personally use is Air Asia but be aware that they have a 15 KG baggage weight limit. At a cost of about USD20, you can get an additional 15 KG if you check in a bag as a SPORTS BAG. Check www.airasia.com where you can book online.

The slower options:
By bus or train

   
PADI Scuba Diving Tips of The Day » When flying after diving within the no-decompression limits, whether using the RDP, or another table or computer, the general rules are: for a single dive you should wait at least 12 hours before flying; for repetitive dives and/or multi-day dives you should wait a minimum of 18 hours. It never hurts to err on the side of caution and wait a little longer.