NGC 3999 (also PGC 37647) is a magnitude +14.7 spiral galaxy located in the constellation Leo.
The galaxy was discovered by Irish astronomer Lawrence Parsons, 4th Earl of Rosse, using a 182.88 cm (72 inch) speculum reflector at Birr Castle on the 25th April 1878.
Right Ascension 11h 57m 56.4s, Declination +25° 04' 06"
