PIC24F16KA101 and interrupts

void Timer1init()
{
    T1CON = 0x00; 			//Stops the Timer1 and reset control reg.
    TMR1 = 0x00; 			//Clear contents of the timer register
    PR1 = 4000;				//Load the Period register with 1mSec counter 
   // PR1 = 16000U;				//Load the Period register with 1mSec counter 
	IPC0bits.T1IP = 0x01; 	//Setup Timer1 interrupt for desired priority level
	// (This example assigns level 1 priority)
	IFS0bits.T1IF = 0; 		//Clear the Timer1 interrupt status flag
	IEC0bits.T1IE = 1; 		//Enable Timer1 interrupts
	T1CONbits.TON = 1; 		//Start Timer1 with prescaler settings at 1:1 and
							//clock source set to the internal instruction cycle
}

volatile int mSecDelayCounter=0;         // used in the millsecond delay function

/* interrupt service routine for Timer1 ISR*/
void __attribute__((__interrupt__, __shadow__)) _T1Interrupt(void)
{
/* Interrupt Service Routine code goes here */
IFS0bits.T1IF = 0; 							//Reset Timer1 interrupt flag														
mSecDelayCounter--;	
}