The hydrogen-bonding interpolymer association between poly(acrylic acid) (PAA) and the poly(N,N-dimethylacrylamide) (PDMAM) side chains of a negatively charged graft copolymer was studied in aqueous solutions. The graft copolymers, P(AA-co-AMPSA)-g-PDMAM, contain 50 wt % PDMAM, while their backbone comprises acrylic acid (AA) and mostly 2-acrylamido-2-methylpropane sulfonic acid (AMPSA) units. The formation, at low pH, of compact and soluble hydrogen-bonding interpolymer complexes between PAA and the side PDMAM chains, is suggested by combining turbidimetry and dilute solution viscosity measurements. Moreover, in semidilute solutions, the pH-controlled association-dissociation of these water-soluble hydrogen-bonding interpolymer complexes results in a spectacular pH-controlled thickening behavior.