Table I. The absolute number of adeno-tonsillar interventions is reported for each unit recruited in the study during the years of the investigation. Overall number of surgical operations has been subdivided for geographical area (northern and southern Italy) and for type of unit (General and Paediatric Units).

	Adeno-tonsillar surgery
	1999	2000	2001	2002	2003	2004	Total
Unit 1 (Conticello - Torino)	72	68	67	98	81	85	471
Unit 2 (Taormina - Torino)	0	0	38	43	54	80	215
Unit 3 (Mira - Pavia)	385	408	433	531	528	590	2.875
Unit 4 (Mevio - Magenta)	304	297	402	306	371	318	1.998
Unit 5 (Tarantino - Genova)	918	901	845	849	837	787	5.137
Unit 6 (Vicini - Forlì)	203	263	253	234	239	164	1.356
Unit 7 (Laudario - Bologna)	254	382	353	445	592	482	2.508
Unit 8 (Casolino - Cesena)	129	136	122	135	144	137	803
Unit 9 (Rinaldi Ceroni - Bologna)	188	179	146	114	201	186	1.014
Unit 10 (Mansi - Napoli)	1320	1357	1315	1222	1168	1059	7441
Unit 11 (Motta Jr - Napoli)	102	113	57	66	64	0	402
Unit 12 (Galli - Napoli)	146	170	121	218	213	284	1152
Unit 13 (Galletti - Messina)	340	103	84	100	135	126	888
Unit 14 (La Rotonda - Matera)	108	118	98	151	111	69	655
Total	4469	4495	4334	4512	4738	4367	26915
Total northern Italy	2453	2634	2659	2755	3.047	2829	16377
Total southern Italy	2016	1861	1675	1757	1691	1538	10538
Total Paediatric Units	2238	2258	2198	2114	2059	1926	12793
Total General Units	2231	2237	2136	2398	2679	2441	14122