Ailbhe O'Driscoll Collins (26), originally from Co Clare and living in Dublin, is in Boston with the Royal College of Surgeons Ireland.
"We're in lockdown in our hotel; there are 10 of us from RCSI over here. We're all accounted for.
"Two of the lads were near the finish line around five minutes before it happened. There were two big bangs and then lots of smoke and people running away.
"We just all got calls from the Irish Consulate and they said they've accounted for all of us from RCSI.
"We're just staying in our hotel rooms and watching it on TV.
"From what I've heard, there are two dead and 23 injured," she said. She said there was a heavy military presence in the build-up to the race and throughout it.
"I was on my final mile and there was a big military guy running alongside so there definitely was an army presence, a massive presence."
Ms O'Driscoll Collins finished the race in a time of three hours 36 minutes.
The last of her group finished 10 minutes later -- minutes before the first explosion.
"There was just under 27,000 runners taking part. It (the bomb) went off right at the finish line, I think that was where the VIPs were sitting -- just on the opposite side."