This paper presents a printed organic complementary technology on flexible plastic substrate with high performance N and P-type Organic Thin Film Transistors (OTFTs), based on small-molecule organic semiconductors in solution. Challenges related to the integration of both OTFT types in a common complementary flow are addressed, showing the importance of surface treatments. Data on single devices and elementary complementary digital circuits (inverters and ring oscillators) are presented, demonstrating that a robust and reliable flow with high electrical performances can be established for printed organic devices.