A third of NHS trusts are breaching waiting times for treating patients - almost four times the number this time last year, figures show.
Data for England reveals 45 primary care trusts (PCTs) did not hit the target in August for treating patients within 18 weeks of referral by their GP.
In August 2010, just 12 PCTS breached the waiting times target.
The NHS as a whole is still meeting a national target for 90% of patients to be seen within 18 weeks, but only because some PCTs are performing much better than others.
The figures for August show that the total number of people who waited 18 weeks or more for treatment reached 28,917, compared to 19,547 in August 2010.
A total of 759 patients waited more than a year, compared with 286 in the previous year.
The number still in the system who have not yet been treated stood at 2.61 million in August, down from 2.65 million in the previous year.
A spokesman for the Department of Health said median waiting times - the exact mid-point in the range of patient waits - remained stable.
He said: "Average waiting times are low and remain stable. The vast majority of patients still receive treatment within 18 weeks.
"We are committed to driving improvements in performance and the quality of care that the NHS provides - including keeping waiting times low."