Medical experts say there's been a four-fold rise in the number of Welsh cases of measles this year, compared to the previous 12 months.
From January to June there were 61 cases.
Public Health Wales says raising MMR vaccination rates is the key to tackling the problem.
Incidences of whooping cough were also up.
More top news
Former Plaid Cymru leader says Parliament and devolved nations must have a say on Brexit or there should be a new referendum
Swansea City failed to capitalise on last weekend's dramatic win over Crystal Palace, as they fell to a heavy 5-0 defeat away at Tottenham.
Post Office workers and managers have held a third strike in a long-running dispute over job losses and pensions.