I had heard several comments from Vietnam Visitors that a Local Guest (female) can not accompany you in a Hotel.

Also told that the local Vietnam Police keep track of your Hotel or Travel stays.

Any truth to any of this ?

The legal situation in Vietnam is that a foreigner may not stay overnight with a Vietnamese citizen of the opposite sex,if they are not married.Having said that,over the last 5 years I have stayed in hotels here with my Vietnamese fiancee on many occasions,and we never had any problems.After we were married we have never been asked for any sort of proof(occasionally the hotel staff would ask my wife if we were married,but once she said Yes,they never asked for any proof of this)It's probably the case that in the more expensive hotels then they might require this,but I think the situation is more relaxed than in the past.However if you turn up with a new friend that you have just met,then there might be problems checking in to one room.As regards the Immigration Dept keeping track of guests,they most certainly do.The hotel will certainly want to see your passport when checking in,and normally they will require to keep it for inspection by the police.They might accept a photocopy,but a lot insist on keeping the passport,this is quite normal practice.

I have been to Vietnam dozens of times both north (Hanoi as well as others areas) and south (HMC)

I have had female friends stay with me in my hotel for both short times and weeks on end with no problems or questions, and I have stayed at my female frends home too with out any questions or problems.

Yes most hotels will take ID or passport, same everywhere, Even my friends who stay. However, I have never had problems or questions with that.

Mostly government hotels will not allow guests in your room after 22:00. What you do in your room up to that time is your own business.

Private hotels may be less bothered but if you check in together it may not be a problem.

I have never been asked for proof of marriage when checking into a privately owned hotel.

HCMC is probably more lax than Ha Noi in following the rules.

Immigration will keep track of your hotel and travel stays, the same as any other country you visit, although registration is reported to the local police, same as other countries.

Thank you all for the answers to my question.