IGT has suffered decreases in revenue, adjusted EBITDA and operating income for 2015.
The results are complicated by GTech's $6.4bn acquisition of IGT, which completed in April 2015, after which the newly enlarged firm assumed the IGT name.
The supplier has therefore provided results on both a reported and pro forma basis.
Pro forma results, which tend to provide a better indication of underlying company performance, represent the combined results of both companies, even though they didn't officially come together until April.
On a pro forma basis, revenue was down 12% year-on-year to $5.09bn, with the decrease equivalent to 4% on a constant currency basis.
Adjusted EBITDA fell16% to $1.7bn, which translated to a downswing of 7% when constant currency is applied.
Adjusted operating income dropped 19% to $1.07bn, or 9% on a constant currency basis.
Operating income decreased 51% to $533m, which equates to 39% when considering constant currency.
Adjusted figures exclude the impact of purchase price amortization, impairment charges, restructuring expense, and certain one-time, primarily transaction-related items, while constant currency changes for 2015 are calculated using the same foreign exchange rates as the corresponding 2014 period.
IGT's net debt at the end of 2015 was $7.71bn, compared to $2.64bn the previous year.
For the fourth quarter of 2014, revenue was down 3% to $1.37bn on a pro forma basis, although actually increased 5% when applying constant currency.
Adjusted EBITDA was unmoved, which equated to an 8% rise on a constant currency basis.
Adjusted operating income was up 9% to $293m, representing a 17% improvement when applying constant currency.
Operating income dropped 26% to $132m, a downturn which lessened to 15% under constant currency.
"We ended a year of transformation with a strong quarter for our lottery and gaming operations, enabling us to reach the high end of our EBITDA guidance," said Marco Sala, CEO of IGT.
"We are confident that we have established a solid foundation from which we can continue to lead the gaming industry and grow our business."
CFO Alberto Fornaro said the results provided evidence of the firm's "financial and operational discipline".
He said: "We achieved our first-year synergy goals three months ahead of plan and have increased our total cost synergy target.
"As we look to 2016, we are forecasting growth for our core operations, while incremental synergies are expected to mitigate certain anticipated headwinds.
"Our financial condition is solid, placing us in a strong position to pursue our growth objectives, continue to reduce debt, and remunerate our shareholders."