Shares slipped more than 5 percent in trading Wednesday.
Some KFC restaurants in the U.K. were forced to temporarily close in February because they ran out of chicken after its new delivery partner DHL was unable to fulfill deliveries.
Same-store sales at KFC in the quarter were up 2 percent, weaker than the 2.6 percent analysts had forecast, according to StreetAccount.
"Adjusting for the impact of this, we estimate Yum same-store sales growth would have been 2 percent and KFC's same-store sales growth would have been 3 percent," David Gibbs, president and chief financial officer at Yum, said during the earnings conference call Wednesday.
The company expects to take an additional hit from the U.K. incident in the second quarter due to a decrease in marketing while some of its locations were shuttered.
On the call, Gibbs said the second quarter will be "the worst quarter of the year, most likely."
In the quarter ended March 31, the company said net income rose to $433 million, or $1.27 per share, up from $280 million, or 77 cents per share, a year earlier.
Excluding items, the company earned 90 cents per share, better than the 68 cents per share analysts in a Thomson Reuters survey had expected.
The company's revenue fell 3 percent to $1.37 billion, compared with $1.42 billion last year. Wall Street had expected revenue to be $1.09 billion, according to Thomson Reuters estimates.
"As we begin the second full year of our transformation journey, I'm pleased with our progress towards becoming a more focused, more franchised and more efficient company," CEO Greg Creed said in a statement Wednesday. "We're maintaining all aspects of our full-year 2018 guidance and remain confident that this transformation is building a strong foundation for long-term growth and will deliver increased returns for our stakeholders."
The company reiterated its forecast that same-store sales will grow 2 to 3 percent this year and that net new unit growth will be 3 to 4 percent.
At this time last year, investors were calling for Yum to divest Pizza Hut. Instead, the company plowed $130 million into new equipment, technology and marketing. The chain also has been heavily discounting its pizza and even launched a new rewards program, to steal market share from competitors like Domino's Pizza and Papa John's.
Despite the investment, Pizza Hut same-store sales were up 1 percent, missing the mark of 1.8 percent that analysts had expected.
"Pizza Hut is a global iconic brand and the recent same-store sales results are simply not acceptable," Creed said on the call.
Meanwhile, Taco Bell beat expectations with growth of 1 percent. Analysts had forecast same-store sales growth of 0.8 percent for the quarter.
While the launch of Nacho Fries created buzz, the popularity of this promotion, as well as other $1 value items, weighed heavily on margins during the quarter.
"I think the good news is that you know we're not a one-trick pony when it comes to value," Creed said on the call. "We've got a lot of really smart plays around value."