LISBON, April 26 (Reuters) - Portuguese telecommunications firm NOS posted on Wednesday a 15% drop in first-quarter net profit as amortisation costs rose after strong investments to massify its fast-speed 5G network.

NOS, whose businesses include cable television and cinemas, made a net profit of 34.9 million euros ($38.55 million) between January and March.

Consolidated revenues rose 2.2% to 381.4 million euros in the quarter from a year ago, of which 369.2 million euros were from its core telecommunications business. ($1 = 0.9052 euros) (Reporting by Sergio Goncalves;Editing by Andrei Khalip)