Abstract: The rather frequent occurrence, and sometimes long duration, of ?-ray events at photon energies above 100 MeV challenges our understanding of particle acceleration processes at the Sun. The emission is ascribed to pion-decay photons due to protons with energies above 300 MeV. We study the X-ray and radio emissions and the solar energetic particles (SEPs) in space for a set of 25 Fermi ?-ray events. They are accompanied by strong SEP events, including, in most cases where the parent activity is well-connected, protons above 300 MeV. Signatures of energetic electron acceleration in the corona accompany the impulsive and early post-impulsive ?-ray emission. ?-ray emission lasting several hours accompanies in general the decay phase of long-lasting soft X-ray bursts and decametric-to-kilometric type II bursts. We discuss the impact of these results on the origin of the ?-ray events.