Banya Bashi mosque, built in 1576 by the great Ottoman architect Sinan, is the only functioning mosque that remains of 500 years of Ottoman domination in Sofia, the capital of Bulgaria

General Mufti's Office of Bulgaria The Muslim population of Bulgaria, including Turks, Muslim Bulgarians, Pomaks, Roma, and Crimean Tatars, lives mainly in northeastern Bulgaria and in the Rhodope Mountains. According to the 2001 Census, the total number of Muslims in the country stood at 966,978, corresponding to 12.2% of the population. According to the criterion of ethnic group they were divided into the following groups: Turks - 713,000; Bulgarians - 131,000; Roma - 103,000; Others - 20,000;

Most of the Bulgarian Muslims are Sunni Muslims as Sunni Islam was the form of Islam promoted by the Ottoman Turks during their five-century rule of Bulgaria (see History of Bulgaria). Shi'a sects such as the Alians, Kizilbashi and the Bektashi also are present, however. About 80,000 Shi'a Muslims live mainly in the Razgrad, Sliven and Tutrakan (northeast of Rousse) regions. They are mainly descendants of Bulgarians who converted to Islam to avoid Ottoman persecution but chose a Shi'a sect because of its greater tolerance toward different national and religious customs. For example, Kuzulbashi Bulgarians could maintain the Orthodox customs of communion, confession, and honoring saints. This integration of Orthodox customs into Islam gave rise to a type of syncretism found only in Bulgaria.

The largest mosque in Bulgaria was the Tumbul Mosque in Shumen, built in 1744.

Like the practitioners of other beliefs including Orthodox Christians, Muslims suffered under the restriction of religious freedom by the marxist-leninist Todor Zhivkov regime which favoured atheism and suppressed religious communities. The Bulgarian communist regimes declared traditional Muslim beliefs to be diametrically opposed to secular communist ideology.

After the breakdown of communism, Muslims in Bulgaria again enjoyed greater religious freedom. Some villages organized Qur'an study courses for young people (study of the Qur'an had been completely forbidden under Zhivkov). Muslims also began publishing their own newspaper, Musulmani, in both Bulgarian and Turkish.

Muslims in Bulgaria in accordance to their ethnic groups

• Turks (612,818)
• Bulgarian Gypsies (112,495)
• Millets (77,712)
• Pomaks (71,978)
• Balkan Gypsies (23,298)
• Bulgarians (18,623)

• Crimean Tatars (5,800)
• Arabs (4,710)
• Ahmadi Muslims (40,000) 
• Eastern Bulgarian Gypsies (2,456)
• Vlach Gypsies (1,463)
• Macedonians (1,020)
• Albanians (876)
• Circassians (512)
• Kurds (190)

Source : http://en.wikipedia.org/wiki/Islam_in_Bulgaria