I am a general surgeon in a Muslim country. I am a Muslim and I would like to study plastic surgery. What is the opinion of our religion in studying and working in such a field?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

Studying medicine in all its fields and forms is Fardh Kifaya (collective duty), i.e. if some Muslim study this science, the others will be free from being sinful.
Studying plastic surgery and what is related to it also comes under the above Islamic fundamental generalization. Sometimes specializing in such a field becomes compulsory on a group of Muslims to satisfy the needs of Muslim community. This means that it is legal to study such a specialization, but this causes, us to seek the Shari'a ruling concerning plastic surgery because some kinds of plastic surgery are permitted while others are forbidden.
Plastic Surgery is of two kinds:
1- A surgery that is done merely for beautification. This kind is Haram, since it is a form of changing the Divine creation. The Prophet (Sallallahu Alaihi wa Sallam) said: "Allah has cursed those females who get their teeth filed for beauty, and thus interfere in Allah's creation" [ Bukhari and Muslim ]
2- A surgery that is done for some need such as removing pain, damage or something, whether it comes into existence by creation or by other means (diseases, accident..). This is legal and Halal both for men and women. In a sound Prophetic Hadith, 'Arfaja Ibn Sa'd (a companion of the Prophet (Sallallahu Alaihi wa Sallam)) had lost his nose on the day of 'al-Kulab'. So, he had nose of silver but it became smelly and stinking. Therefore, the Prophet ordered him to have a nose made of gold.
Ibn Jarir al-Tabari said: 'A woman is not permitted to change anything of Allah's creation with the exception of something that causes harm, such an extra or abnormal tooth, or an extra finger that causes pain. Man is like woman in this concern.
For more details, check 'al-Mufassal', a book by Abdul Karim Zaidan .
Allah knows best.